get_security_group() now returns rules

get_security_group() previously only returned a security_group's id,
name, tenant_id, and description. This patch changes get_security_group()
to also return the security_group_rules associated with the security group.
Fixed bug 1103278

Change-Id: Iebc0022faa5c7072380d52b81c13783add0f4d46
Merge "get_security_group() now returns rules"