(maint) Stop leaking file handles

File.new(f) results in a file handle being used. The test manifest in
this case ended up leaking file handles which caused the master to run
out of file handles while serving a request. This lead to a consistent
failure on the first thread requesting the catalog where the error
reported was:

Could not autoload puppet/type/notify: no such file to load -- /usr/lib/ruby/site_ruby/1.8/puppet/type/notify.rb

The error was misleading. The underlying problem was not an ENOENT, but
an EMFILE (Too many open files). By switching to File.read(f) the
manifest will no longer leak file handles.