elog-gen.py : implement error inheritance

If an error inherits another error (via the error YAML interface), have
the child error inherit parent's metadata. Only single inheritance is
supported as of now.

Change-Id: I9ff295f4db04a9c5389f66e04f5d28287f9628a9
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
3 files changed