Validated xenial queries:

# Pre-release 
$ lxc exec test-xenial -- dpkg-query --show cloud-init
cloud-init	0.7.9-153-g16a7302f-0ubuntu1~16.04.2
$ lxc exec test-xenial -- python3 -c 'import sys;
from cloudinit.util import is_resolvable_url;
print(is_resolvable_url(sys.argv[1]))' http://ubuntu.com


# from dns-masq
dnsmasq[27789]: query[A] does-not-exist.example.com from 10.249.77.13
dnsmasq[27789]: forwarded does-not-exist.example.com to 127.0.0.53
dnsmasq[27789]: query[AAAA] does-not-exist.example.com from 10.249.77.13
dnsmasq[27789]: forwarded does-not-exist.example.com to 127.0.0.53
dnsmasq[27789]: query[A] example.invalid from 10.249.77.13
dnsmasq[27789]: forwarded example.invalid to 127.0.0.53
dnsmasq[27789]: query[AAAA] example.invalid from 10.249.77.13
dnsmasq[27789]: forwarded example.invalid to 127.0.0.53
dnsmasq[27789]: query[A] example.invalid from 10.249.77.13
dnsmasq[27789]: forwarded example.invalid to 127.0.0.53
dnsmasq[27789]: query[AAAA] example.invalid from 10.249.77.13
dnsmasq[27789]: forwarded example.invalid to 127.0.0.53
dnsmasq[27789]: query[A] T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj.foo from 10.249.77.13
dnsmasq[27789]: forwarded T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj.foo to 127.0.0.53
dnsmasq[27789]: query[AAAA] T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj.foo from 10.249.77.13
dnsmasq[27789]: forwarded T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj.foo to 127.0.0.53
dnsmasq[27789]: query[A] T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj from 10.249.77.13
dnsmasq[27789]: forwarded T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj to 127.0.0.53
dnsmasq[27789]: query[AAAA] T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj from 10.249.77.13
dnsmasq[27789]: forwarded T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj to 127.0.0.53
dnsmasq[27789]: query[A] T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj from 10.249.77.13
dnsmasq[27789]: forwarded T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj to 127.0.0.53
dnsmasq[27789]: query[AAAA] T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj from 10.249.77.13
dnsmasq[27789]: forwarded T77S9LM0QtKKC9WnG96MbWLQlRWgt5hj to 127.0.0.53
dnsmasq[27789]: query[A] ubuntu.com from 10.249.77.13
dnsmasq[27789]: cached ubuntu.com is 91.189.94.40
dnsmasq[27789]: query[AAAA] ubuntu.com from 10.249.77.13
dnsmasq[27789]: forwarded ubuntu.com to 127.0.0.53
dnsmasq[27789]: query[A] test-xenial.foo from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial.foo to 127.0.0.53
dnsmasq[27789]: query[AAAA] test-xenial.foo from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial.foo to 127.0.0.53
dnsmasq[27789]: query[A] test-xenial from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial to 127.0.0.53
dnsmasq[27789]: query[AAAA] test-xenial from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial to 127.0.0.53
dnsmasq[27789]: query[A] test-xenial from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial to 127.0.0.53
dnsmasq[27789]: query[AAAA] test-xenial from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial to 127.0.0.53
dnsmasq[27789]: query[A] test-xenial.foo from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial.foo to 127.0.0.53
dnsmasq[27789]: query[AAAA] test-xenial.foo from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial.foo to 127.0.0.53
dnsmasq[27789]: query[A] test-xenial from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial to 127.0.0.53
dnsmasq[27789]: query[AAAA] test-xenial from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial to 127.0.0.53
dnsmasq[27789]: query[A] test-xenial from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial to 127.0.0.53
dnsmasq[27789]: query[AAAA] test-xenial from 10.249.77.13
dnsmasq[27789]: forwarded test-xenial to 127.0.0.53


--- updated cloud-init xenial 
$ lxc exec test-xenial -- dpkg-query --show cloud-init
cloud-init	0.7.9-233-ge586fe35-0ubuntu1~16.04.1

$ lxc exec test-xenial -- python3 -c 'import sys;
from cloudinit.util import is_resolvable_url;
print(is_resolvable_url(sys.argv[1]))' http://ubuntu.com

--- from dns-masq
dnsmasq[27789]: query[A] does-not-exist.example.com from 10.249.77.13
dnsmasq[27789]: forwarded does-not-exist.example.com to 127.0.0.53
dnsmasq[27789]: query[AAAA] does-not-exist.example.com from 10.249.77.13
dnsmasq[27789]: forwarded does-not-exist.example.com to 127.0.0.53
dnsmasq[27789]: query[A] example.invalid from 10.249.77.13
dnsmasq[27789]: forwarded example.invalid to 127.0.0.53
dnsmasq[27789]: query[AAAA] example.invalid from 10.249.77.13
dnsmasq[27789]: forwarded example.invalid to 127.0.0.53
dnsmasq[27789]: query[A] example.invalid from 10.249.77.13
dnsmasq[27789]: forwarded example.invalid to 127.0.0.53
dnsmasq[27789]: query[AAAA] example.invalid from 10.249.77.13
dnsmasq[27789]: forwarded example.invalid to 127.0.0.53
dnsmasq[27789]: query[A] __cloud_init_expected_not_found__.foo from 10.249.77.13
dnsmasq[27789]: forwarded __cloud_init_expected_not_found__.foo to 127.0.0.53
dnsmasq[27789]: query[AAAA] __cloud_init_expected_not_found__.foo from 10.249.77.13
dnsmasq[27789]: forwarded __cloud_init_expected_not_found__.foo to 127.0.0.53
dnsmasq[27789]: query[A] __cloud_init_expected_not_found__ from 10.249.77.13
dnsmasq[27789]: forwarded __cloud_init_expected_not_found__ to 127.0.0.53
dnsmasq[27789]: query[AAAA] __cloud_init_expected_not_found__ from 10.249.77.13
dnsmasq[27789]: forwarded __cloud_init_expected_not_found__ to 127.0.0.53
dnsmasq[27789]: query[A] __cloud_init_expected_not_found__ from 10.249.77.13
dnsmasq[27789]: forwarded __cloud_init_expected_not_found__ to 127.0.0.53
dnsmasq[27789]: query[AAAA] __cloud_init_expected_not_found__ from 10.249.77.13
dnsmasq[27789]: forwarded __cloud_init_expected_not_found__ to 127.0.0.53
dnsmasq[27789]: query[A] ubuntu.com from 10.249.77.13
dnsmasq[27789]: forwarded ubuntu.com to 127.0.0.53
dnsmasq[27789]: query[AAAA] ubuntu.com from 10.249.77.13
dnsmasq[27789]: forwarded ubuntu.com to 127.0.0.53
dnsmasq[27789]: reply ubuntu.com is 91.189.94.40