(PE-6012) HTTP client should use :localcacert

When we create the SSL context for Ruby Puppet to use for outgoing
requests, we need to be using the :localcacert instead of the :cacert
because :cacert doesn't necessarily live on the master, and even
then they might be different.
Merge pull request #193 from nwolfe/pe6012-localcacert-not-cacert

(PE-6012) HTTP client should use :localcacert