tests: Add "create email test"

[sebastian at sspaeth.de]

tests: Add "create email test"

I just pushed this test (commit 2800a71) to the next branch.

This is the first test that actually creates a (local) email
and syncs. We check the result of the sync operation, to see
if the server has actually been assigning a proper UID to the
email and bail out if not.

This test therefore excercises our ability to properly detect the
new UID of an APPENDED email. Obviously we still need some
IMAP<->IMAP tests too, but since this is the same codepath being
used for APPENDs in that case, it could also help to detect
instabilities there.

In order to get this test in, the OLITestLib got a few new helper
functions:
- delete_maildir
- create_mail
- get_maildir_uids

The test passes here. I invoke it via:

python -m unittest
test.tests.test_01_basic.TestBasicFunctions.test_04_createmail

or run python setup.py test, to run the whole suite.

Signed-off-by: Sebastian Spaeth <Sebastian at SSpaeth.de>