(#158) (#166) Resolve issue loading bundler from gem installs
(#158) (#166) Resolve issue loading bundler from gem installs

This changes the method for resolving the installation path of a user
managed bundler gem to make it not depend on bundler itself.

Also cleans up the management of subprocess PATH from SDK-319.

DavidS/pdk,DavidS/pdk,DavidS/pdk