Add ceph support for centos based images

[phlogistonjohn]

Ensure ceph support exists in the centos based images. Ceph support (for the samba vfs module and sambacc) was already present in the Fedora based images due to (a) fedora packages cephs in the main repos (b) the samba and sambacc RPMs having correct dependencies, as long as the proper samba vfs modules are selected. These changes will enable ceph libraries to be installed on the samba server image when based on centos and works around some issues in the sambacc dependencies as well.

Add a new package source called "devbuilds" that is valid for centos based images. It enables both the samba nightly builds repo (like the existing "nightly" package source) as well as dev builds from ceph's main branch.

In order to do this cleanly the script and images are refactored slightly to re-organize how packages are selected for install.

Finally, enable ceph builds from the reef branch on centos nightly - note that there's a bug in the current version of reef that prevents the client from talking to newer mds servers but that will eventually get resolved (Hopefully).

[mergify[bot]]

This pull request now has conflicts with the target branch. Please resolve these conflicts and force push the updated branch.

[phlogistonjohn]

I added a new intro paragraph to the description. I hope that helps.

[phlogistonjohn]

@synarete would you mind approving if you're OK with my earlier responses?