[bluez] Avoid sporadic call hold indicators. Fixes JB#11820.

Call hold indicators were updated every time call property state
was received over D-Bus. This causes extra indicators for the cases
two calls are present. Fix by flagging calls to wait status update
and only send call indicator when new call statuses are known.
Merge pull request #19 from hmallat/telephony-no-sporadic-hold-indicators

[bluez] Avoid sporadic call hold indicators. Fixes JB#11820.