tests: Better tolerate file system restriction on file name length.

tests: Better tolerate file system restriction on file name length.

ecryptfs on Linux restricts file names to 143 bytes, but these two tests
used a 150-byte name.  This commit fixes the specific problem on ecryptfs
by reducing the name it test to 143 bytes.  It also fixes the more general
problem of name length restrictions by skipping the test, rather than
failing it, if a directory with the 143-byte name cannot be created, since
the most likely problem is that the name is too long for the file system.

Reported-by: Zoltán Balogh <zoltan.balogh@ericsson.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>