Don't rely on implicit operator comparison

Json has a bunch of implicit overloaded operators for comparing
vectors/arrays/maps with their json counterparts.  Unfortunately, when
used in unit tests, these cause warnings in clang, so update the code to
use the ElementsAre check from gmock.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I658557cb59d568fd50cf6f3bef73d6f90b5c56cf