Don't use copy_to_filename in filestorage tests.

There's a separate test for it already in test_file_storage.py, and when
the fixture gets reused in parallel-throughput tests, that specific setting
causes big trouble.
Merge branch 'switch-to-instance-collection'

In particular, this changes kvlayer.client() to use the global yakonfig
configuration and not take an explicit config parameter.
Merge remote-tracking branch 'origin/master' into nonuuid-swtic
link to github issue