add Runnable.globals(arr) method for per test global whitelist

Instead of suite wide whitelisting of global leaks, this allows for
individual tests to whitelist globals. This allows for keeping global
detection for tests which are not expected to set globals while allowing
for certain globals if the author expects a test to set globals
Merge pull request #1046 from defunctzombie/per-test-globals

add Runnable.globals(arr) method for per test global whitelist