Fine tune btif config mechanism to limit the number of section in bt config...

Fine tune btif config mechanism to limit the number of section in bt config cache and improve the bt config clone performance

* Bt config cache will grow bigger and bigger without limitation and
cause many Bluetooth stability issues
* Do not clone the whole config cache before writing config cache
into file, clone paired devices section instead.
* Implement BtifConfigCache class to handle bt devices config add,
remove, paired, unpaired,..etc.

Bug: 143515989
Test: 1. Add BtifConfigCacheTest unit tests to test bt config cache
setup, paire with a new devices, unpaire with a devices, remove the
sections with specific key.
2. Checking the paired devices information still existed in settings
after Bluetooth disable or device reboot.
3. Checking the paired devices information still saved in btif_config
file after Bluetooth disable and device reboot.
4. Remove btif_confing files and enable Bluetooth, checking the
btif_config file can be created and included adapter information
normally.
5. Checking the paired devices information be clean in btif_config
file after device factory reset
6. keep BLE scanning, then pair with a bluetooth device, connect a
bluetooth device, disable Bluetooth, checking the function work
normally.
Tag: #stability

Change-Id: Ide1ba1b6daaf9d102ab96976cbf28e65031423d0