Repeat metalava errors at the end to make it easy to find them

Also suppress "unresolved import" messages.

Bug: 161374683
Test: Introduce a lint error, run "m update-api" and make sure the
    error shows up at the end.
Change-Id: Ib5250f7f9593dc4f89f9e7f6dc614e230a966e8f

java/droiddoc.go

@@ -1519,7 +1519,9 @@ func metalavaCmd(ctx android.ModuleContext, rule *android.RuleBuilder, javaVersi
 	cmd.Flag("--no-banner").
 		Flag("--color").
 		Flag("--quiet").
-		Flag("--format=v2")
+		Flag("--format=v2").
+		FlagWithArg("--repeat-errors-max ", "10").
+		FlagWithArg("--hide ", "UnresolvedImport")
 
 	return cmd
 }