packaging: engine-backup: Safer password input
packaging: engine-backup: Safer password input

Allow passing db password also interactively and using an environment
variable, in addition to using a file and using a command line option.

Bug-Url: https://bugzilla.redhat.com/1002401
Change-Id: Icbc497af2653417beab54a9be307332cdf69a48a
Signed-off-by: Yedidyah Bar David <e7f2f616ce8817ad893bbeaad3e942e94c69d323@redhat.com>

yingyun001/ovirt-engine,OpenUniversity/ovirt-engine,yapengsong/ovirt-engine,zerodengxinchao/ovirt-engine,walteryang47/ovirt-engine,eayun/ovirt-engine,walteryang47/ovirt-engine,halober/ovirt-engine,yingyun001/ovirt-engine,yapengsong/ovirt-engine,walteryang47/ovirt-engine,walteryang47/ovirt-engine,halober/ovirt-engine,zerodengxinchao/ovirt-engine,yingyun001/ovirt-engine,OpenUniversity/ovirt-engine,zerodengxinchao/ovirt-engine,yingyun001/ovirt-engine,eayun/ovirt-engine,OpenUniversity/ovirt-engine,yingyun001/ovirt-engine,halober/ovirt-engine,yapengsong/ovirt-engine,zerodengxinchao/ovirt-engine,walteryang47/ovirt-engine,eayun/ovirt-engine,eayun/ovirt-engine,halober/ovirt-engine,zerodengxinchao/ovirt-engine,yapengsong/ovirt-engine,eayun/ovirt-engine,OpenUniversity/ovirt-engine,yapengsong/ovirt-engine,OpenUniversity/ovirt-engine