gluster: interpret and use correct xml elements

xml output of rebalance and remove-brick status returns filesSkipped
in <skipped> tag and value of <statusStr> tag cleaned up to use it as
proper enum.

Change-Id: I9b90283ac2b9f4b54acfccffa02a30e38e5e9d85
Signed-off-by: Bala.FA <barumuga@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19674
Reviewed-by: Dan Kenigsberg <danken@redhat.com>