kdump: Fix version comparisons

Use rpmUtils.miscutils.compareEVR for correct package version
comparisons.

This should work:
  '2.0.0-273.el6' < '2.0.0-273.1'
  '2.0.0-273.1.el6' >= '2.0.0-273.1'
  '2.0.0-274.el6' >= '2.0.0-273.1'

Change-Id: Ica14bd688c73a511ad8d7557231cff2e184830a9
Bug-Url: https://bugzilla.redhat.com/1079821
Signed-off-by: Martin Perina <mperina@redhat.com>