Fix mocha adapter not reporting all test results

By commit 6c890dc, reporting test result is delayed by setTimeout,
which may cause inconsistent order of event emitting, such as firing
"test-result" event after "all-test-results" event fired.

This commit prevents firing "all-test-results" if any test reporting is
delayed, so that we can always get "all-test-results" event after all of
"test-result" events have been fired.
Merge pull request #324 from kotas/fix-mocha-incomplete

Fix mocha adapter not reporting all test results