Fix comments about System Functions

This commit fixes comments about "System Functions".
 * Add a missing comment about System Functions in the header
 * Fix singular to plural like others

Change-Id: I3feb94cd11a6683ca80093574d60fdf7420e3af2
Savanna: use heat infra engine if available

In Savanna we have two provisioning engines:

* "savanna" that directly work with nova/neutron/glance/cinder/etc and
   we'd like to deprecate it early in Juno release cycle, but it's still
   useful due to the fact that it could work ok w/o Heat;
* "heat" engine uses Heat for provisioning of cluster resources, it's
   currently under active development and we're ready to make it default
   for OpenStack installations with enabled Heat.

Change-Id: I937337b3921e9e51768a118fb4b6bd95962622bd
Merge "Fix comments about System Functions"
Merge "Savanna: use heat infra engine if available"