(QENG-751) Request for Higgs support in installing beaker

- adds install_higgs command
- executes against master node
- downloads pe packages based upon pe_ver/pe_dir
- goes up to the point in the install where human interaction is
  required (notices indication in install log that a link has been
  provided to a web server)
I'd rather either see `#do_higgs_install` exposed as part of the API, or else allow `#install_higgs` to take a parameter to choose the install location.  The pattern we're encouraging for using the new installer on split deployments is actually not to put the Higgs server on the (to-be) master, but on the console node. (See "General Prerequisites and Notes" [here](http://docspreview1.puppetlabs.lan/pe/latest/install_pe_split.html)).  Also, a separate Higgs server (somewhat incorrectly referred to as the "jump box") should also be supported.