Make lots of tests run in parallel

Putting t.Parallel() in each test makes them run in parallel.
Additional t.Parallel() could be added to each subtest, although
that requires making a local copy of the loop variable for
table driven tests.

Test: m checkbuild
Change-Id: I5d9869ead441093f4d7c5757f2447385333a95a4
diff --git a/apex/vndk_test.go b/apex/vndk_test.go
index 60b6ed5..e623990 100644
--- a/apex/vndk_test.go
+++ b/apex/vndk_test.go
@@ -9,6 +9,7 @@
 )
 
 func TestVndkApexForVndkLite(t *testing.T) {
+	t.Parallel()
 	ctx, _ := testApex(t, `
 		apex_vndk {
 			name: "myapex",
@@ -62,6 +63,7 @@
 }
 
 func TestVndkApexUsesVendorVariant(t *testing.T) {
+	t.Parallel()
 	bp := `
 		apex_vndk {
 			name: "myapex",