log about what agent binary is being downloaded is clumsy

[John A Meinel]

If you do "juju bootstrap --debug" you end up with this line:
10:15:00 INFO juju.cloudconfig userdatacfg_unix.go:355 Fetching agent: curl -sSfw 'tools from %{url_effective} downloaded: HTTP %{http_code}; time %{time_total}s; size %{size_download} bytes; speed %{speed_download} bytes/s ' --retry 10 -o $bin/tools.tar.gz <[https://juju-dist.s3.amazonaws.com/tools/agent/2.1-rc2/juju-2.1-rc2-ubuntu-amd64.tgz]>

While it's *super* nice to be able to see what concrete binary was downloaded, the syntax around all of that is terrible. 'Fetching agent' with a curl line that has a bunch of % escapes just feels bad. Having it be just:

Fetching agent: https://juju-dist.s3.amazonaws.com/tools/agent/2.1-rc2/juju-2.1-rc2-ubuntu-amd64.tgz

Would be a lot more useful.

If we want to print the 'curl' commandline to aid in debugging, that may be fine, but the above really feels awkward to get there.

[Anastasia (anastasia-macmood)]

This is a duplicate of bug # 1492530. Marking it as such.