We have removed CentOS 7 from nodepool now we can stop mirroring
pacakges for it. This deletes official CentOS 7 package mirror content
and OBS packages mirrored by the OpenSUSE mirror script for CentOS 7.
A followup change will remove the OpenSUSE mirroring entirely as this
was the last thing it was used for.
Change-Id: I484651b0845eaab933e98106684e0a2a6215b3d7
6df6c6507f