android/tester: Fix for not checking for BT_STATUS_SUCCESS

For BT_STATUS_SUCCESS no checks were done as it is 0 in bt_status_t
enum. Valid status for no status expected should be STATUS_NOT_EXPECTED.
android/tester: Fix bluetooth disable success test case

This fixes not checking for proper status on bluetooth disable.
android/tester: Add start device discovery success test case

Add test case for starting device discovery with success.
android/tester: Add stop device discovery done test case

Add test case for stopping device discovery when it wasn't started.
android/tester: Add device discovery cancel success test case

Test for successfull discovery canceling after it was started.
android/tester: Add start device discovery done test case

This tests device discovery start being reported as done because of
ongoing discovery.
android/bluetooth: Fix sending invalid RSSI device property

RSSI property is of int32_t type but int8_t was send in durring
remote devices discovery.
android/AVDTP: Add avdtp_add_disconnect_cb and avdtp_remove_disconnect_cb

With these functions the user application can detect when the AVDTP has
been disconnected and cleanup properly.
android/A2DP: Use avdtp_add_disconnect_cb to cleanup on disconnect

This replaces the use of g_io_add_watch with avdtp_add_disconnect_cb so
connection tracking stay within AVDTP code.
android/AVDTP: Add avdtp_shutdown

avdtp_shutdown can be used to disconnect closing all existing stream
properly.
android/A2DP: Fix disconnecting after AVDTP session creation

Once the connection is handover to AVDTP code the GIOChannel can be
unref but it should not close the connection.
emulator: Add new method for adding l2cap server

This method allow user to add l2cap server and register
connect callback. If no callback is specified, it will behave
like bthost_set_server_psm() method.
emulator/bthost: Make bthost_add_l2cap_conn return the added struct for convenience
emulator/bthost: Remove double lookup with bthost_find_l2cap_cb_by_psm
tools/l2cap_tester: Add read client test case

This test case send data from remote device to client.
It verifies if data is passed corerctly through L2CAP socket.
tools/l2cap_tester: Add write client test case

This test case write data from client to remote server.
tools/l2cap_tester: Add read server test case

This test checks data transfer from remote client to server.
tools/l2cap_tester: Add write server test case

These test case send data from local server to remote client.
tools/l2cap-tester: Fix checking for write() return values
tools/l2cap-tester: Fix checking for read() return values