[PATCH aeolus-cli] BZ#747719 error message for image import with incorrect parms

[Maros Zatko]

https://bugzilla.redhat.com/show_bug.cgi?id=747719

This patchset is without test.
I'm sending it just in case we don't have tests ready today.
If we do, there will be other patchset with tests included, sent by Petr.

Sorry for any inconvenience,
Maros