Extends COMMIT parameters with git hash in make system

We can define the exact commit hash or branch that
want to use for building packages from.

Value should be defined in config.mk with format:
 REPONAME_COMMIT?=branch
  or
 REPONAME_COMMIT?=hash
for example:
 FUELLIB_COMMIT?=stable/5.1
 FUELLIB_COMMIT?=203ef3179007cffe3236032e61ecbaf1cd20605f

Change-Id: Ifa225003f03dfa41028abb6db0a5ac83ad22f81e
Close-bug: #1364076
Merge "Extends COMMIT parameters with git hash in make system"