Add test of cwd to resmoke tests

Make a dumb sanity-test that asserts that the cwd is the mongo repo root. Perhaps also import key modules to detect the user not pip install-ing the right things. The goal is to help users that use IDEs that assume the cwd should be the buildscripts directory or something else; this otherwise results in cryptic error-messages. Ensure this is the first test run by naming the file something like test_AAA_sanitycheck.