Introduced Active device for volume updates and volume update in pause state

1.(a) For absolute volume change from DUT side the device which gets the volume
updates is 'active device'. In case of 2 headsets both supporting Absolute
volume (maintaining different volume granularity) in Multicast/SoftHand-off
scenario sending different volume updates to DUT simultaneously because of
DUT receiving different feedback from individual Headsets(old cached map value).
Hence we are maintaining only one device active at a time for these volume
updates.
(b) In non-multicast scenario we are making the device active on the basis of
their ConnectionState Change(single connection) and later A2dpAudioState change
if other device comes into picture(SoftHand-off case).
(c) In multicast scenario we are making the device active which is first one
to go for A2dpAudioState change. If second device connects then we disable the
support of absolute volume. If later on any device disconnects we make active
device to other one which is left in the connection.

2. Changed send update in volume (DUT triggered) to a check based on number of
connected devices instead of playing devices for getting volume updates.

CRs-Fixed: 1046431
Change-Id: I00e00bfcb160e02669884cf4207565e52589a599