[PATCH 00/12] run more generic tests on TEST_DIR

[Christoph Hellwig]

As Stanislav pointed out previously various tests worked fine on NFS
when it still defined a scratch dir that we abused for the test dir.

This series makes various tests that don't require specific file system
sizes or parameters run on TEST_DIR instead of using the scratch devices.

This also allow to remove various bits of boilerplat code as the TEST_DIR
is always available, and checked after each test.