Rename mk2rbc/cmd to make `go install` work properly

The standard go tooling assumes that a package's binary name should be
the name of the containing folder. Before this change, `go install` or
`go build` (without `-o`) names this binary `cmd`.

Test: treehugger
Change-Id: I45a4e97f4a0d59744d644e30636250ceefe3bd1c
diff --git a/soong_ui.bash b/soong_ui.bash
index 1d027c4..8e7cd19 100755
--- a/soong_ui.bash
+++ b/soong_ui.bash
@@ -33,8 +33,8 @@
 source ${TOP}/build/soong/scripts/microfactory.bash
 
 soong_build_go soong_ui android/soong/cmd/soong_ui
-soong_build_go mk2rbc android/soong/mk2rbc/cmd
-soong_build_go rbcrun rbcrun/cmd
+soong_build_go mk2rbc android/soong/mk2rbc/mk2rbc
+soong_build_go rbcrun rbcrun/rbcrun
 
 cd ${TOP}
 exec "$(getoutdir)/soong_ui" "$@"