Skip invariant checking and adding when nothing provided

Change-Id: Icc3dca675820d331fb1d6e8f3a5a4169d1b2d113
Add more requirements to cover tox environment

To see how code is really covered we should run as much tests as
possible in cover environment, so we should use dependencies from
the most reach environment. Currently it's py27-sa9-ev.

Change-Id: I7af092f4789b167dad1fba20b5b267f99a741b0e
Put full set of requirements to py26, py27 and py33 envs

pyXY envs are considered to be default, so they must have richest set
of test requirements.

Change-Id: Ide2a8ab0500c0c6769ad7b8f0cc76f229a83db60
Merge "Add more requirements to cover tox environment"
Merge "Put full set of requirements to py26, py27 and py33 envs"
Merge "Skip invariant checking and adding when nothing provided"