Disable nbmand tests on kernels w/o support

Disable nbmand tests on kernels w/o support

This change allows mountpoint_003_pos and send-c_props
to run on Linux kernels that do not support mandatory
locking. Linux kernel versions greater than or equal to
4.4 no longer support mandatory locking and the test
suite will now account for that.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Closes #6346
Closes #6347
Closes #6362