yum grouplist response on F20 is lower case

On el6 the `yum grouplist` response contains
'Installed Groups:' but on F20 it is 'Installed groups'.

This change modifies to regexp in the slave.pp to accept both.

Change-Id: I50d80d7a11bee4437ed3967dc1a55ef56d15ba8c
Merge "yum grouplist response on F20 is lower case"