Add centos builder.
Add centos omnibus builder.
Add enchant for sphinxcontrib-spelling.
Don't include commented find-links in ubuntu pip.conf.
Use elrepo kernel (for 3.17+).
Use same version of zfs on centos, as on fedora.

We need this for the new kernel.
Bump ZFS/SPL version on centos.
Add a note about needing to upgrade docker.
Merge forward.
Add additional docker image to centos base image.
Upstream has released docker 1.3.2.

This reverts commit 84ed97da2f9b15510d0cabd6fed80b266383cbc1.
Merge pull request #46 from ClusterHQ/centos-builder-FLOC-1024

[FLOC-1054] Add a CentOS 7 builder.