* Check if BUILDHISTORY_DIR exists before doing anything with it, in
case no tasks that would have created it have executed
* Ensure the git repo in BUILDHISTORY_DIR is initialised with "git init"
before attempting to do anything with it
* Check if any files have been added or changed before adding and
committing, to avoid an error from "git commit"
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
