test: more robust test runner method checks
test: more robust test runner method checks

The test runner context may have many different custom assertion
methods defined by spec tests. This patch allows us to arbitrarily
add new context methods to any number of subclasses of the
TestRunnerContext and still determine that they are test runner
"methods".

mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native