Rename check method to isBlockedNumber.

+ Clearer name about functionality, and async nature.
+ Change it to return "false" if it fails and is trying to block an
invalid number, rather than returning "true". This matches a more
standard success/fail return paradigm.
+ Update logic for showing "invalid" message based on return value.
+ Simplify parameter set which it takes in; always take nubmer and
countryIso, because they can be used to calculate the normalized #.

Bug: 25343277
Change-Id: If6fb28a6395e207047f4b27bfac37f5c70a9bac3