Restore the Centos7 Dockerfile from 20107f73414eba825fd855a34a076776fc6b1da8 along with a new functional test
Add centos dependencies
Merge remote-tracking branch 'origin/master' into centos-omnibus-package-FLOC-1000

Conflicts:
	admin/test/test_packaging.py
flake8 fixes
Use common Docker and ZFS dependency wrappers
Use generic contact address
Force the use of centos 7 image.
Use the virtualenv/pip from centos/epel.
Pip from CentOS's virtualenv isn't new enough.
Address review comments.
Address review comments.
Merge pull request #1005 from ClusterHQ/centos-omnibus-package-FLOC-1000

[FLOC-1000] CentOS omnibus package builder

Authors: @wallrj, @tomprince
Reviewers: @tomprince, @exarkun