Versioning for ostf tests

During development of new releases we may introduce new sets of tests that simply
wont work on older environments. Since we support master node upgrade, we need to exclude those tests
from test runs.

It can be done with:

1. Flexible versions comparators , e.g 2014.*-6.* > *-6.*
It will require modifying docstring and designing such comparator

2. Distributing tests for each release, e.g tests for 2014-2-6.0 will be in separate directory,
and when ostf will be invoked to run tests for specific release, it will check version of cluster release, and discover tests
of correct version.

Affected patches:

  neutron tests - Change-Id: I8cd108156c95b119b11e84f772280846b7953d6b
  ceilometer tests - Change-Id: I4f488166223ca6bbd294815e6bff7215ad6009ba