webadmin: Rename 'Server' to 'Host' in Add Brick pop up

 Renaming the label 'Server' in Add Bricks pop up to 'Host'.
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1023956

Change-Id: I691880731320b132c664578e5ce9288ab2e4b533
Signed-off-by: Ramesh Nachimuthu <rnachimu@redhat.com>