separate builds for testing and flake8

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
speed up builds by caching apt

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
make this bastard work

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
do not run coveralls there

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
one more `||true`

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Set travis to run tests in Polish.

RATIONALE: Spanish has twenty locales.  It takes a while to generate them.
           I replaced it by Polish which has just one.  (I could’ve chosen
           another language that is supported by us and has just one
           locale, but I chose mine for no reason at all.  I’m no patriot,
           don’t think this was the reason.)

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
save even more time

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Optimize the test suite.

Changes include:

 * default tests locale is Polish instead of Spanish

   Rationale: see commit 049f59a.

              tl¹;dr: 1 vs 20 locales to generate, that’s all.

 * flake8 is running on its own build jobs.

   Rationale: we are now able to tell what passed and what didn’t at a
              glance.  We do not have to search through stuff to find out
              what (nosetests or flake8) failed.

 * Use the Travis apt cache, which will save us a few seconds here or
   there.

¹ This commit message is actually longer than the one in 049f59a.

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Merge pull request #888 from getnikola/optimize-tests

Optimize tests