goma_ctl.py ensure_start in Soong UI.

As suggested in b/118390303#comment18, let me run
"goma_ctl.py ensure_start" in soong UI.

Bug: 118390303
Test: stop compiler_proxy, and execute following command:
Test: USE_GOMA=true lunch aosp_arm-eng
Test: and confirms compiler_proxy is running.
Change-Id: I859daae6ae2399c5b6bce2fafd874dfdb7c6aae0
Signed-off-by: Yoshisato Yanagisawa <yyanagisawa@google.com>

ui/build/Android.bp

@@ -47,6 +47,7 @@ bootstrap_go_package {
         "environment.go",
         "exec.go",
         "finder.go",
+        "goma.go",
         "kati.go",
         "ninja.go",
         "path.go",