test: Unify all tests to use the pass_if_equal function.

test: Unify all tests to use the pass_if_equal function.

Previously some tests (dump/restore) were doing ad-hoc verification of
values and their own printing of PASS/FAIL, etc. This made it
impossible to count test pass/fail rates in a single place.

The only reason these tests were written that way was because the old
execute_expecting function only worked if one could directly test the
stdout output of a notmuch command. The recent switch to pass_if_equal
means that all tests can use it.