misc/android: copy testdata directories to device before running

We've got away with not copying the testdata directories for the
standard library because the exec wrapper also pushes almost the
entire $GOROOT tree to the device, including testdata directories.

Similar to what the iOS exec wrapper does.

Change-Id: I91ef63ef84a658fc8843002890132c64b7c1d20e
Reviewed-on: https://go-review.googlesource.com/c/163626
Run-TryBot: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/android/go_android_exec.go

@@ -95,6 +95,7 @@ func main() {
 	} else {
 		adbSyncGoroot()
 	}
+	run("shell", "mkdir", "-p", deviceCwd)
 
 	// Binary names can conflict.
 	// E.g. template.test from the {html,text}/template packages.
@@ -102,6 +103,10 @@ func main() {
 	deviceBin := fmt.Sprintf("%s/%s", deviceGotmp, binName)
 	run("push", os.Args[1], deviceBin)
 
+	if _, err := os.Stat("testdata"); err == nil {
+		run("push", "testdata", deviceCwd)
+	}
+
 	// Forward SIGQUIT from the go command to show backtraces from
 	// the binary instead of from this wrapper.
 	quit := make(chan os.Signal, 1)