Update Cisco package repo setup parameters

Cisco OpenStack Installer recently introduced a change to remove
redundancy in the package repository setup routines used to set
up both the package repositories set up by Puppet agents running
on already-provisioned nodes as well as those introduced as part
of the preseed template for nodes being provisioned by Cisco's
hooked-in Cobbler process.  This patch creates a mapping between
parameters that should be set to the same values in the coe and
coi classes, sets nonvendor defaults in common.yaml, and provides
vendor overrides in vendor/cisco_coi_common.yaml.
It also substantially beefs up the inline comments to make it more
apparent to the end user what these settings are doing.

Change-Id: I4dd37e8a3ae2d3a23c7a2886c2233e7c5e29e96f
Partial-Bug: #1269856
Merge "Update Cisco package repo setup parameters"