add database packages for ubuntu

adding mysqlclient-dev and pq-dev so that pip installs will work.
Refactor openstack_git_repo & add openstack_commit

It will become more and more important to have more information about
individual commits to an openstack repo.  Therefore, add the
OpenstackCommit class. Refactor OpenstackGitRepo to accomodate this.
Do not include editables in pip dependencies

There is no point in including pip editables in the pip dependendies, so
remove them.
Fix pep8 issue in util.py

Another extra space
Add system dependencies to fpm package creation

There are many times when we want to have system-level dependencies that
are prerequisites for the package we just built. Update the Package
class to allow for this.
Add gerrit_dependencies setting

Allow the user to specify whether they want the pip dependencies to be
pulled from Gerrit.
Support user-specified version

It would be helpful to have a version that is passed in on the command
line...especially with things like Jenkins build numbers.
Rework package_builder

A bunch of updates to package_builder:
- remove source from the package
- better support Gerrit dependencies
- pass system dependencies into Package