cask plugin to add cask to $PATH
plugin was lacking setting {}_HOME variables for all gvm installed
binaries, this fixes that.

This also sets JAVA_HOME (only tested on OSX).
silly mistake, forgot this is a soft link and needed to follow the link
removing `-e` tests when cheking for `-f` or `-d`

adding local variable flag and setting the variable if java home isn't
taken care of in the first if check.

For some reason there were different tab widths for this bottom
section, unifying to what the top was at -- 2 spaces.
Merge pull request #275 from jacobono/gvm-update-and-cask-plugin