core: block migration for paused VM due to EIO only

We used to block migration for VMs which are paused because of any
reason other than NOERR. From now on, we will allow to migrate paused
VMs if their pause reason is different than EIO, and only for those that
are paused because of EIO we will block migrations.

Change-Id: I68f238330b30f21aef070d99431e951cf9ef5c84
Bug-Url: https://bugzilla.redhat.com/1099506
Signed-off-by: Arik Hadas <ahadas@redhat.com>