Modified configuration group name to lowercase

Most of the OpenStack project makes use of lower case for
configuration group names. But, 'neutron' was having group
names in either cases. Bug states it is fine to have group
name in upper case for [DEFAULT] but needs to be changed
for others. It was noted that [PLUMgridDirector] was having
characters.

Change-Id: I95f2dad6d5ae17f722202f4917b6ef460cd41e15
Closes-Bug: #1176683
Merge "Modified configuration group name to lowercase"