fix loggregator package name

Signed-off-by: Alex Suraci <asuraci@pivotallabs.com>
move $GOROOT out of params and into script

this is a system-level config for the build, not a parameter to tweak on
a run-by-run basis. having it as a param means environment variables will pass
through, which we obviously don't want.

Signed-off-by: Alex Suraci <asuraci@pivotallabs.com>