bluetooth: provide dbus property State

- provide dbus property named State to check if
  bluetooth available or connected
- clean code

tower: https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/477d0eaaf5cc47bc8e2b664e3e098a4a/
Change-Id: I0eb2ac92a1aa20306b24ae241dd63156523ba8cd