Install script updates

Some bug fixes and updates to the `install.sh` script:
 - Ensure `wget` is available.
 - Don't assume home directory is that of `ec2-user`.
 - Make sure `GRAILS_HOME` and `PATH` are set properly even if grails was already there and not downloaded by the script.
 - Pass `JAVA_OPTS` to `grails` so we can use a proxy.
 - Don't clone ice into the home directory if we're not running the script in there.