Clean up tox.ini and make tempest and unit test distinct

This commit creates a separate base env for tempest tests and
tempest's unit tests. However, to keep the same interface the tempest
env is setup by overloading the testenv using substitution from a
common base section.

As part of this internal reorganization in the tox.ini several other
things are cleaned up or removed. Usless or duplicate job definitions
are removed. The unit tests are switched to pretty_tox. Previously
they were run without any output which made it difficult to figure out
exactly what was running. Additionally, this removes the unnecessary
regex filter on the unit test job. The unit tests use a different
discovery path so there is no need to also filter it on the same path
this will allow the use of more specific regexes with tox to filter
tests.

Change-Id: I996d81dec2739bbe907f5fe87a335994c01697b3
Merge "Clean up tox.ini and make tempest and unit test distinct"