failsafeUndeployment is unhelpful when using dropins

[Azquelt]

Issue Overview

When using failsafeUndeployment, if the container is unable to delete the app archive, it doesn't raise an exception and marks the file for deletion at the end of the test.

However, failing to delete the application archive results in the application not stopping, so the test fails saying "application did not stop" with no information about the underlying cause

Expected Behaviour

Either test should not fail, or the failure message should say that the application file could not be deleted.

Current Behaviour

Test fails because the application did not stop

Steps To Reproduce

1. enable failsafeUndeployment with dropins
2. use another process to lock application archive file while the test is running