Storing SNMPd credentials in Ceilometer

-We need to store SNMPd credentials for readnonly user for
 Overcloud nodes, so Ceilometer can poll the nodes for statistics.

Change-Id: I077250b6cae307159366319364cf044ed1f96d71
Name sysctl.d files with .conf

The files in /etc/sysctl.d should always be suffixed
with a .conf extension.

Change-Id: I5868f87a1ad90eb41c421f73611e77ec6ea07484
Update bootstack to use sysctl-set-value.

Updates install.d/01-boot-stack to use the sysctl element
to make sysctl config changes.

Change-Id: I697b95c8a5a71856638b43bcc2e60b7c61030ea3
Merge "Name sysctl.d files with .conf"
Merge "Update bootstack to use sysctl-set-value."
Merge "Storing SNMPd credentials in Ceilometer"