qa, test: run unit tests for cephfs.pyx with non-root user

qa, test: run unit tests for cephfs.pyx with non-root user

Run test_python.sh with non-root user. This makes it necessary to change
the owner user and group of file system root to be same as this non-root
user. This brings testing closer to the real-world scenario and also
allows exercising negative tests where an FS op would fail for a non-root
user but it would pass for root user.

There are few tests that exercise FS operations where root user is
needed. Group these tests under a separate class and add extra code for
this class that allows these tests to run with root UID and GID.

Signed-off-by: Rishabh Dave <ridave@redhat.com>