Remove setup_test_env() because removing this methods removes an extra
layer of abstraction which makes tests more readable. Rename
_create_client_and_keyring_file() to just _create_client() and reverse
the order of parameters in remount_with_new_client() and set default
value of cephfs_mntpt to '/'.
Signed-off-by: Rishabh Dave <ridave@redhat.com>