vdsm: migration progress: count memRemaining also

Take into account that not only dataRemaining can grow, but memRemaining
can it too. So, we should check both of them.

+ make code slightly more readable.

Signed-off-by: Peter V. Saveliev <peet@redhat.com>
Change-Id: I92f37a507ead4cccf835302d25cd02eb344bbcb1
Reviewed-on: http://gerrit.ovirt.org/15124
Tested-by: Martin Polednik <mpoledni@redhat.com>
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>