this patch adds 'GlusterServer' related schema in qapi/block-core.json

[Jeff: minor fix-ups of comments and formatting, per patch reviews]
Signed-off-by: NPrasanna Kumar Kalever <prasanna.kalever@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-id: 1468947453-5433-5-git-send-email-prasanna.kalever@redhat.com
Signed-off-by: NJeff Cody <jcody@redhat.com>