Added auto-detection of the javaws path for Windows machines

[mhenderson-so]

This involved changing the existing const's to functions, but the end effect is the same.

I have also govendor'd in external dependancies, as there was a bug fix needed for the github.com/howeyc/gopass package, as its syntax had been updated and was a breaking change. Unfortunately github.com/howeyc/gopass also vendors in a large chunk of golang.org/x/ packages.

Sadly none of these fix the fact that on the newer firmwares on iDracs, passing through a raw username/password in the jnlp file doesn't work