Added compatibility for ppc64le and not having required repo
Added compatibility for ppc64le and not having required repo

Script will now check for the existence of the openpower repo and
download it if it is not present in the workspace. Script will verify 
the type of system the script is running on to modify the dockerfiles
so that they can run on ppc64le systems. Updated the dockerfiles to use
latest as their tags. Updated a few comments as well.

Change-Id: Ied3cdba8c28d7ff9a1b24be69bb6d8df11772be2
Signed-off-by: Alanny Lopez <1a0708d0a8bc975c5c0d676d544b3b68a25ff13b@ibm.com>

openbmc/openbmc-build-scripts,openbmc/openbmc-build-scripts