Maid 198 drive filesystem test torn down issue

https://maidsafe.atlassian.net/browse/MAID-198

double free issue during testing environment torn down is resolved
termination and dump file issue during testing environment torn down is resolve
The error message to FUSE is critical (FUSE is terminated)
However the upper layer code will catch the error thrown from FUSE and handle it
(continue with normal tear down process)
So no harm to testing / production code