restapi: Refactored BackendGlusterBrickResource

Refactored BackendGlusterBrickResource to use parent's
populateAdvancedDetails method to populate brick with
advance details in case of All-Content set to true.

Change-Id: I70354105b57159e6ba872804701910b4111b734b
Signed-off-by: Sahina Bose <sabose@redhat.com>