Disable VM notification for blocked numbers.

+ Added a utility to do a synchronous lookup for whether a number is
blocked, but it should not be used normally from the UI thread.
+ Change voicemail notifier code to obtain countryIso, and pass back
list of calls to notify as list (to make it easier to remove elements).

Bug: 23944007
Change-Id: Iad1f8ee200b8f8734be3db0504482fcdee61e412