Revert "engine: Use isBlockDomain() where possible"

This is a partial revert of the rest parts of commit
f4eaef896d8927f968023c01e36db173c3deb73d

It was commit without the proper review, and should never have been
merged.

Change-Id: I181986b7ead007e0193d48253261132554a7f69b
Signed-off-by: Allon Mureinik <amureini@redhat.com>