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

xml/xml_test.go

@@ -78,6 +78,7 @@ func assertEqual(t *testing.T, name, expected, actual string) {
 
 // Minimal test
 func TestPrebuiltEtcXml(t *testing.T) {
+	t.Parallel()
 	ctx := testXml(t, `
 		prebuilt_etc_xml {
 			name: "foo.xml",