fstests: Make ./new work for non-root user

fstests: Make ./new work for non-root user

Currently 'new' script sources common/config which tries to find
mkfs and fails if not found (which is likely for non-root user).
This is inconvenient as development usually does not happen as root.
In fact the vast majority of setup in common/config and common/rc is
not necessary for 'new'. Split out the necessary bits into new
common/test_names and use it in 'new'. Cleanup common/rc and
common/config now that they're only used from 'check' and 'setup'.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>