Fix nailgun task check before backup/restore

* Adds check to restore
* Fixes typo in command 'fuel task'

Change-Id: Ice725d93ba7ffa674d3bdf74a9decb1a80762a54
Closes-Bug: #1352847
(cherry picked from commit 27df393db262314613fffbfc551b844fcc648005)
Merge "Fix nailgun task check before backup/restore" into stable/5.1