kdump: Check for crashkernel param

Adds check for crashkernel command line parameter. If it's not present,
kdump detection cannot be configured.

Change-Id: Ie83efd12c8763f2336506fa61c34c38d7fc9bfe8
Bug-Url: https://bugzilla.redhat.com/1079821
Signed-off-by: Martin Perina <mperina@redhat.com>