(#6364) Adjust mis-translated regex in mount provider for AIX

The commit to simplify the regex used to parse the output from the mount
command on AIX (50c12e55b6f8462f6904ae061e661d1d10c7590a) mis-translated
it.

The original regex was grabbing the 3rd space-separated element, not the
2nd. This mis-translation caused the provider to grab the device
information instead of the mount point, and compare that to the desired
mount point. This would cause Puppet to think that the mount was never
actually mounted under normal circumstances.

The code from 50c12e5 was passing the tests because the fixture data did
not include the mandatory leading whitespace that the original regex was
looking for. The updated fixture data is pulled from the mount manpage
from AIX v6r1.

Reviewed-by: Paul Berry <paul@puppetlabs.com>