UX: more readable error message checking space

Changed the error message when there's not enough space
for the self hosted engine VM to be more readable.

Change-Id: I56d5e011377f6f5bd43b4c86fceb57b6e622ff9d
Bug-Url: https://bugzilla.redhat.com/1013662
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>