Report atime and relatime as the property's actual value.

Neither atime nor relatime should be considered to be "temporary mount
point properties". Their semantics are enforced completely within ZFS
and also they're (correctly) not documented as being temporary mount
point properties.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2257