This commit adds testing for the gentoo element based off of the debian
element. In adding testing support a couple of additional errors were
found and corrected, namely the following.
* shm is not in /proc/mounts though it is valid for use based off of
the sticky flag.
* The path in ELEMENTS_PATH needs to be pruned to be usable.
* Added uuidgen-runtime to the list of packages installed for Ubuntu
as the new ubuntu-trusty image does not ship with it.
Change-Id: I0d2768a912b350e1b2cf40d2fd227fdc767b1bcb
