Comment 0 for bug 1661337

In some cases we have transient network failure while attempting to recv gpg keys when configuring apt.

https://jenkins.ubuntu.com/server/job/curtin-vmtest/737/artifact/output/XenialTestAptSrcDisablePockets/logs/install-serial.log

[ 40.161264] cloud-init[1528]: Command: ['gpg', '--keyserver', 'keyserver.ubuntu.com', '--recv', '0E72 9061 0D2F 6DC4 D65E A921 9A31 4EC5 F470 A0AC']
[ 40.162213] cloud-init[1528]: Exit code: 2
[ 40.163711] cloud-init[1528]: Reason: -
[ 40.164256] cloud-init[1528]: Stdout: "gpgkeys: key 0E7290610D2F6DC4D65EA9219A314EC5F470A0AC can't be retrieved\n"
[ 40.174200] cloud-init[1528]: Stderr: 'gpg: requesting key F470A0AC from hkp server keyserver.ubuntu.com\ngpg: no valid OpenPGP data found.\ngpg: Total number processed: 0\ngpg: keyserver communications error: keyserver helper general error\ngpg: keyserver communications error: unknown pubkey algorithm\ngpg: keyserver receive failed: unknown pubkey algorithm\n'
[ 40.180654] cloud-init[1528]: During handling of the above exception, another exception occurred:
[ 40.182056] cloud-init[1528]: Traceback (most recent call last):
[ 40.183644] cloud-init[1528]: File "/curtin/curtin/gpg.py", line 65, in getkeybyid
[ 40.185067] cloud-init[1528]: recv_key(keyid, keyserver=keyserver)
[ 40.186653] cloud-init[1528]: File "/curtin/curtin/gpg.py", line 48, in recv_key
[ 40.187895] cloud-init[1528]: (key, keyserver, error))

Curtin should retry this command.