Fixup tests to work on CentOS 5

Several tests were failing because the depended on being able to find a
user provider. On CentOS 5 this didn't work because the provider that
should be used (the useradd provider) is not considered suitable when it
gets run as a non-privaleged user because the useradd and related
commands are not executable.

The user_spec.rb and group_spec.rb test didn't need the tests that were
failing because they were testing functionality that is already tested
by the Type base class's own tests.

The ral_spec.rb needed more mocking of the things it was using in order
to abstract it from the system on which it is running.

The resources_spec.rb got a small cleanup and was fixed by reordering
the data loading in Puppet::Type::Resources so that it doesn't load
information about a user until it needs to.