Replace mock DatabaseManager with TestDatabaseManager

Sometimes mock instances are not working correctly when it is
accessed by multithread which is one of the cause of flaky tests.
This CL replaces the use of the mock DatabaseManager with the
TestDatabaseManager class in ActiveDeviceManager.

Bug: 289954923
Test: atest BluetoothInstrumentationTests:ActiveDeviceManagerTest
Change-Id: I7e0b6db6ce80d80aa8d0ab3b971cd0e3f4c8ca69