config: added backward compatibilty
config: added backward compatibilty

Added backward compatibility supporting upgrade from
3.1 version which used the keyword rhevm instead of engine.
The old config files will be backed up during the upgrade.

Change-Id: I781493d9a224e412edbf1816579718de39ce0f54
Signed-off-by: Sandro Bonazzola <fcb014d63786651910af5db2ecc5316c668188ef@redhat.com>

oVirt/ovirt-log-collector,oVirt/ovirt-log-collector,oVirt/ovirt-log-collector