Protect Drive test operations from being run at runtime

All operations from the org.nuxeo.drive.operations.test package, event though they are restricted to administrators with Automation bindings, should only be runnable in test mode.

For each of them let's raise an Exception if org.nuxeo.runtime.testing is not set to "true" (Framework#isTestModeSet).

This is a quickfix, real solution would be to have a dedicated (and private) marketplace package to be deployed only within Drive integration tests.