Improve nfs-server to support multiple shares and options

With this we aim at making the nfs-server element capable of
deploying an arbitrary number of shares and to define for each
a list of clients allowed and the respective export options.

Change-Id: Ib056885c94c3bc475ed0e84237c83414795fc8e0
Make rdo-release install safe

Like the epel element, this may be applied to a system that already
has rdo-release installed.  If that happens yum exits non-zero
because for some reason it considers "nothing to do" to be an error.

This simply checks for the existence of the rdo-release rpm before
attempting to install it.

Change-Id: I5867ca074cc1afa843ef1e0f85c1c9b6f2deb403
Remove pip install --pre

We were installing some packages with support for prerelease versions in
expectation of needing it in our CI. This turns out to not be needed so
we should remove it.

Change-Id: I7ae440d3534e33144942c2230a88cf54f8a153d3
Merge "Improve nfs-server to support multiple shares and options"
Merge "Make rdo-release install safe"