HfpClientConnectionService does not synchronize state

Currently active device is a synchronizable state and the current
implementation was simply waiving it. Also the mechanism to create a
phone account was invalid since the PhoneAccountHandle was not unique
per device. PhoneAccountHandle not being unique is OK for now but fails
in case of multiple devices.

Bug: b/28068989
Change-Id: I729df5aa110a428b8ce23cf6658d81c5acbc16a2