Bluetooth: Multiple gatt service for same service on the device support

Added the following support to allow the creation of multiple
gatt services for the same service on the same device:
1. BluetoothGattService maintains a serviceId which is used
to differentiate the gatt service object on the remote
for the same service
2. The service tracker in BluetoothService that maintains the
gatt service <-> callback mapping takes in object path concatenated
with the serviceId as the key so that we can differentiate
the gatt service to route the callback
3. All the asynchronous gatt client methods stores the serviceId
along with the object path as user data
4. Indications and notifications are routed to all the applications
that registered for the watcher on the characteritics
5. The characteristics watcher is deregistered only when all the
applications who registered for it called deregister
6. Disconnection is initiated on the device only when all the
gatt services on the device are closed.

Change-Id: I149f135a6e4f99cd7fd44a9cf7a059562df93ed8
CRs-fixed: 426328