Add -bootclasspath and -classpath flags to the gomobile tool. In a follow-up CL, the gobind gradle plugin will use them to support R and databinding classes from Go. Change-Id: Id33acf0c3fe1ec3908740b2a736ed241fa6391c2 Reviewed-on: https://go-review.googlesource.com/30092 Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>