[xenial] Handle import_ok exception during upgrade

[redshiftzero]

Description

After upgrade to xenial, a one-time unhandled exception (about a successful gpg key import) occurs in a thread the first time gpg decryption occurs on the application server. This was found by @emkll during review of #4094. It does not cause an OSSEC alert or a regression in functionality, but we should see if we can handle it regardless.

Part of #3204.

Steps to Reproduce

0. Provision staging VMs
1. Submit a document as a source
2. Upgrade to xenial via sudo do-release-upgrade (some nice steps thanks to @zenmonkeykstop here)
3. make build-debs-xenial
4. scp the securedrop-app-code deb into app-staging and install it
5. Submit another document as a source

Expected Behavior

No tracebacks appear in /var/log/apache2/source-error.log

Actual Behavior

[Tue Feb 05 21:18:53.367308 2019] [wsgi:error] [pid 4478:tid 3513516791552] Exception in thread Thread-10:
[Tue Feb 05 21:18:53.367335 2019] [wsgi:error] [pid 4478:tid 3513516791552] Traceback (most recent call last):
[Tue Feb 05 21:18:53.367340 2019] [wsgi:error] [pid 4478:tid 3513516791552]   File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
[Tue Feb 05 21:18:53.367351 2019] [wsgi:error] [pid 4478:tid 3513516791552]     self.run()
[Tue Feb 05 21:18:53.367355 2019] [wsgi:error] [pid 4478:tid 3513516791552]   File "/usr/lib/python2.7/threading.py", line 754, in run
[Tue Feb 05 21:18:53.367358 2019] [wsgi:error] [pid 4478:tid 3513516791552]     self.__target(*self.__args, **self.__kwargs)
[Tue Feb 05 21:18:53.367361 2019] [wsgi:error] [pid 4478:tid 3513516791552]   File "/usr/local/lib/python2.7/dist-packages/pretty_bad_protocol/_meta.py", line 670, in _read_response
[Tue Feb 05 21:18:53.367365 2019] [wsgi:error] [pid 4478:tid 3513516791552]     result._handle_status(keyword, value)
[Tue Feb 05 21:18:53.367368 2019] [wsgi:error] [pid 4478:tid 3513516791552]   File "/usr/local/lib/python2.7/dist-packages/pretty_bad_protocol/_parsers.py", line 995, in _handle_status
[Tue Feb 05 21:18:53.367371 2019] [wsgi:error] [pid 4478:tid 3513516791552]     raise ValueError("Unknown status message: %r" % key)
[Tue Feb 05 21:18:53.367374 2019] [wsgi:error] [pid 4478:tid 3513516791552] ValueError: Unknown status message: u'IMPORT_OK'
[Tue Feb 05 21:18:53.367379 2019] [wsgi:error] [pid 4478:tid 3513516791552] 

Comments

See my comments here.