Fix soong for go test ./...

Fix various issues that prevent building or running tests with the
Go tools:

Remove testing/test_spec_proto/go.mod.  There's already a go.mod at
the top level, and adding testing/test_spec_proto/go.mod breaks
compiling with the Go tools in IntelliJ or from the command line.

Fix go vet issues when trying to print []DataPath.

Fix aconfig_conversion_test.go and add it to Android.bp so it runs
in presubmit.

Test: go test ./...
Change-Id: I18af2f05631446fe507744a2951e4b02c7ab59be
diff --git a/cc/cc_test.go b/cc/cc_test.go
index 794c5ee..e2dba90 100644
--- a/cc/cc_test.go
+++ b/cc/cc_test.go
@@ -720,7 +720,7 @@
 		return
 	}
 	if len(testBinary.dataPaths()) != 1 {
-		t.Errorf("expected exactly one test data file. test data files: [%s]", testBinary.dataPaths())
+		t.Errorf("expected exactly one test data file. test data files: [%v]", testBinary.dataPaths())
 		return
 	}
 
@@ -777,7 +777,7 @@
 		t.Fatalf("expected exactly one output file. output files: [%s]", outputFiles)
 	}
 	if len(testBinary.dataPaths()) != 2 {
-		t.Fatalf("expected exactly one test data file. test data files: [%s]", testBinary.dataPaths())
+		t.Fatalf("expected exactly one test data file. test data files: [%v]", testBinary.dataPaths())
 	}
 
 	outputPath := outputFiles[0].String()
@@ -3332,7 +3332,7 @@
 		t.Errorf("expected exactly one output file. output files: [%s]", outputFiles)
 	}
 	if len(testBinary.dataPaths()) != 1 {
-		t.Errorf("expected exactly one test data file. test data files: [%s]", testBinary.dataPaths())
+		t.Errorf("expected exactly one test data file. test data files: [%v]", testBinary.dataPaths())
 	}
 
 	outputPath := outputFiles[0].String()