ceph-disk:  OSD hotplug fixes for Centos

Two fixes for Centos 6.3 and other systems with udev versions
prior to 172.  The disk peristant name using the GPT UUID does
not exist, so use the by_path persistent name instead for the
journal symlink.

The gpt label fields are not available for use in udev rules. Add
ceph-disk-udev wrapper script that extracts the partition
type guid from the label and calls ceph-disk-activate if it is
a ceph guid type. (Bug #4632)

Signed-off-by: Gary Lowell  <gary.lowell@inktank.com>