packaging: engine-service: rework start pid file handling

There is no reason to force user to explicit stop and start the service
in case pid file contains non running process.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=838527
Change-Id: I8d8a7f8f8b7f5941f447df3d279686b973b5c393
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>