Description of problem:
When someone tried to run engine-backup without necessary parameters lead to many error in terminal.

[root@pk-rh35 ~]# engine-backup --mode=backup
FATAL: --file is missing
readlink: missing operand
Try `readlink --help' for more information.
/usr/bin/engine-backup: line 1398: : No such file or directory
Notifying engine
/usr/bin/engine-backup: line 1465: : No such file or directory
/usr/bin/engine-backup: line 1398: : No such file or directory
readlink: missing operand
Try `readlink --help' for more information.
/usr/bin/engine-backup: line 1398: : No such file or directory
Notifying engine
/usr/bin/engine-backup: line 1465: : No such file or directory
/usr/bin/engine-backup: line 1398: : No such file or directory
readlink: missing operand
Try `readlink --help' for more information.
/usr/bin/engine-backup: line 1398: : No such file or directory
Notifying engine
/usr/bin/engine-backup: line 1465: : No such file or directory
/usr/bin/engine-backup: line 1398: : No such file or directory
readlink: missing operand
.... (infinity repeated) ....

After specify all necessary parameters everything works

Version-Release number of selected component (if applicable):
rhevm-3.6.0-0.11.master.el6.noarch

How reproducible:
always

Steps to Reproduce:
1. Have an engine 
2. command "engine-backup --mode=backup" (without --scope, --file, --log)

Expected results:
Warning about missing necessary parameters