apmanager: abstraction for AP service.

Add an abstraction for AP service, which creates/manages hostapd process.
Update org.chromium.apmanager.Manager.CreateService method to be asynchronous,
where the service dbus path is return when the respective Service and Config
object completes the DBus interface registration.

While there, correctly register DBus object interfaces for each dbus object.

BUG=chromium:431760
TEST=unittests
CQ-DEPEND=CL:229600,CL:229430

Change-Id: I5bfb775d2cedb4d636b4f6963795c0d9180cc840
Reviewed-on: https://chromium-review.googlesource.com/229463
Reviewed-by: Paul Stewart <pstew@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Tested-by: Peter Qiu <zqiu@chromium.org>
Commit-Queue: Peter Qiu <zqiu@chromium.org>
18 files changed