restapi: Activate the bricks after data migration

Activates the set of bricks of data migration is over on them. If user
decide to retain the set of bricks for further use, this action can be
invoked.

Usage:
    api/clusters/<cluster-Id>/glustervolumes/<volume-id>/bricks/activate

Input Parameters:
    <action>
        <bricks>
            <brick>
                <name><Brick1-Name></name>
            </brick>
            <brick>
                <name><Brick2-Name></name>
            </brick>
        </bricks>
    </action>

Change-Id: Iee2e7234ac2ca78b741bac12d53fc6441d8c7d80
Signed-off-by: Shubhendu Tripathi <shtripat@redhat.com>