fixed comment in freespace fact to be accurate
Remove require facter from tests.

Handled in spec_helper.
Added fact to check for sudo rights.

It is, in theory, possible to have a system where:

1. sudo isn't installed
2. sudo is installed, but root isn't configured with sudo rights

Thus, I need to confine my postgres space used fact to only work on
systems where sudo works, because it will require sudoing to
pe-postgres.