go/package/gopackages: update gopackages to use the new tool library for its main function
go/package/gopackages: update gopackages to use the new tool library for its main function

Change-Id: I06f13024c021d14e4a759ca9ec24aa54f9d1b97f
Reviewed-on: https://go-review.googlesource.com/c/154558
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools