(maint) log uid and gid for Puppet::Util::Execution.execute if specified as non-default

This might be able to use a little bit of cleanup, I guess it depends on how nicely you want the output formatted. But I was debugging a custom provider that uses Puppet::Util::Execution.execute and seemed to be executing as root instead of the specified user... and found that the debugging output didn't really help me find the problem.
This view doesn't show it, but there's some extra whitespace here. You can see it if you do:

<pre>
$ git show --check 23092882cdb67aa436e910b4a4bc7cd0d5840c3e
...
lib/puppet/util/execution.rb:176: trailing whitespace.
+    
</pre>