After PR #116, it's possible to inject an existing combined_ca_bundle
to the keymanager initialisation. However, it won't work for multiple
users because the file is removed when the keymanager is destroyed.

Considering there's no sensitive data on the file and it's created
as a temp file, we don't need to handle its deletion.

- refresh random key in random time
- add get key by fingerprint
- refactor nicknym methods to own file
- tests

- note this do not include a check for
revoked key, since that need some changes
in gnupg

- Related: #6089

The setUpEnv and tearDownEnv methods are configured to run on
setUpClass/tearDownClass. Some testing systems as trial don't support that,
and that seems to cause some confusion in some systems, causing double
attempts to setup or teardown, and thus failing intermitently.

This commit removes the extra call to setUpEnv and tearDownEnv on tests on
this repository, as it now uses py.test to run tests, which supports
setUpClass and tearDownClass.