[bluez] Work around non-atomic ofono ReleaseAndAnswer. Fixes JB#11816.

Ofono ReleaseAndAnswer method is implemented so that the second call
state becomes incoming before first call becomes disconnected; this
causes bluetoothd to emit RING signals while the first call is still
considered ongoing.

Workaround the problem by calling Hangup and Answer separately instead
of using ReleaseAndAnswer.
Merge pull request #20 from hmallat/telephony-release-and-answer-workaround

[bluez] Work around non-atomic ofono ReleaseAndAnswer. Fixes JB#11816.