engine: Simplify canDoAction

Simplify canDoAction to fast-fail so that the code becomes easier to
read (less nested conditionals).

Change-Id: I7fa092ce8f568b11ae14ac1c943107a10cffa068
Bug-Url: https://bugzilla.redhat.com/907155
Signed-off-by: Mike Kolesnik <mkolesni@redhat.com>