Updates tox.ini to use new features

Reasons:
 - tox update v1.6

Changes:
 - tox 1.6 allows us to skip the sdist step, which is slow.
 - It also allows us to override the install line. In this case, it's
   important as it allows us to stop getting pre-release software we
   weren't asking for.

Original patch by Monty Taylor, talked about here:
http://lists.openstack.org/pipermail/openstack-dev/2013-September/015495.html

Change-Id: I3d857f8ef19b49e0a09b50a9eda7121b28329532
Updates .gitignore to ignore *.egg*

Reasons:
 - pbr-*.egg* is created during tox testing
 - To ignore any package being generated in future

Changes:
 - *.egg* is added in .gitignore
 - python_troveclient.egg* is removed as *.egg*
   takes care of this too.

Change-Id: Ib66bdca8d8d632e88e22cc533d7591613b87123b
Closes-Bug: #1259221
Merge "Updates .gitignore to ignore *.egg*"