Drop setuptools_git dependency

Since https://review.openstack.org/#/c/30522/ was merged into pbr,
setuptools_git is no longer needed.

Change-Id: If8121273f30524de26eb0d6f2b128a369c2c535e
Updates documentation for tox use

In order to create a virtualenv with tox, a postgresql package is needed
as a prerequisite. The dev-quickstart documentation has been updated to
reflect this.

In addition, the prerequisites for Fedora/RHEL were modified, because
mysql-devel is needed, not mysql-libs.

Fixes bug: #1227390

Change-Id: Ibfdb0a9a3d560fcc3fb7d95aaa1d765ed18215e2
Merge "Updates documentation for tox use"
Merge "Drop setuptools_git dependency"