Fix ganglia cookbook plugin system and layer awareness.

cr https://cr.amazon.com/r/1616809/

group conditional into block

cr https://cr.amazon.com/r/1616809/
Fix stop ganglia client conditional
change yum.conf instead of replacing it
Enabling a mount point (i.e. writing /etc/fstab) does not depend on /etc/mtab entry.
Chef 0.9 seems to ignore duplicate resources - work around that for fstab entry.
Stricter dependency flow to avoid race conditions between blkid and mkfs.