[admin CLI integration testing] securedrop-admin update

[redshiftzero]

Description

We should have integration tests for the securedrop-admin update command. This command has a lot of unit tests, but the tests do a lot of mocking out of subprocess calls, I recommend examining those first.

Parent ticket: #3341

[kushaldas]

While working on the integration test, I can see that gpg is sometimes failing to reach any keyserver, and throwing some cryptic error messages. Retrying the same a few times solved the issue.

INFO: Verifying signature on latest update...
gpg: directory '/tmp/.gnupg' created
gpg: keybox '/tmp/.gnupg/pubring.kbx' created
gpg: keyserver receive failed: Cannot assign requested address
gpg: keyserver receive failed: Cannot assign requested address
ERROR (run with -v for more): Command '['timeout', '45', 'gpg', '--recv-key', '--keyserver', 'hkps://hkps.pool.sks-keyservers.net', '22245C81E3BAEB4138B36061310F561200F4AD77']' returned non-zero exit status 2

While searching the error term, I found many other folks saw the same error message, one such example.

@redshiftzero @emkll please let me know your suggestions.

[kushaldas]

I have code ready for PR, but, the above mentioned error is showing up randomly.