AdapterStateChange and HciDeviceChange callback

 * Move observers to main.
 * Add dbus callback util.
 * Use UpstartInvoker instead of NativeSubprocess.
 * Fix multiple issues.

Bug: 189501676
Tag: #floss
Test: cargo test
Test: run btmanagerd and try sending dbus commands
Change-Id: Ie0a678a6f5622221f5d12bb2b8b82a72971ab949