Qualify `ufw` commands

This pull request qualifies the `ufw` commands in order to ensure that they run
without error during a Puppet run. Previously, the command would fail to run as
the exec was unqualified, and Puppet could not find the executable.

Puppet refuses to trust that the $PATH of the shell from which a Puppet run is
started is correct. It therefore demands qualified `exec` types.
Merge pull request #1 from alphagov/qualify-ufw-path

Qualify `ufw` commands