Revert "Make lots of tests run in parallel"

This reverts commit 323dc60712.

Reason for revert: Possible cause of test instability
Bug: 170513220
Test: soong tests

Change-Id: Iee168e9fbb4210569e6cffcc23e60d111403abb8

cc/genrule_test.go

@@ -30,7 +30,6 @@ func testGenruleContext(config android.Config) *android.TestContext {
 }
 
 func TestArchGenruleCmd(t *testing.T) {
-	t.Parallel()
 	fs := map[string][]byte{
 		"tool": nil,
 		"foo":  nil,
@@ -79,7 +78,6 @@ func TestArchGenruleCmd(t *testing.T) {
 }
 
 func TestLibraryGenruleCmd(t *testing.T) {
-	t.Parallel()
 	bp := `
 		cc_library {
 			name: "libboth",