Tweak Soong install rules logging

The make counterparts print a colon, so match that

Change-Id: I9482a0e66b03ad41a66df09d29e76b465ece35c5
diff --git a/android/makevars.go b/android/makevars.go
index 5165a55..0800190 100644
--- a/android/makevars.go
+++ b/android/makevars.go
@@ -471,7 +471,7 @@
 			fmt.Fprintf(buf, " %s", dep.String())
 		}
 		fmt.Fprintln(buf)
-		fmt.Fprintln(buf, "\t@echo \"Install $@\"")
+		fmt.Fprintln(buf, "\t@echo \"Install: $@\"")
 		fmt.Fprintf(buf, "\trm -f $@ && cp -f %s $< $@\n", preserveSymlinksFlag)
 		if install.executable {
 			fmt.Fprintf(buf, "\tchmod +x $@\n")
@@ -515,7 +515,7 @@
 			fromStr = symlink.absFrom
 		}
 
-		fmt.Fprintln(buf, "\t@echo \"Symlink $@\"")
+		fmt.Fprintln(buf, "\t@echo \"Symlink: $@\"")
 		fmt.Fprintf(buf, "\trm -f $@ && ln -sfn %s $@", fromStr)
 		fmt.Fprintln(buf)
 		fmt.Fprintln(buf)