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

java/plugin_test.go

@@ -20,6 +20,7 @@ import (
 )
 
 func TestNoPlugin(t *testing.T) {
+	t.Parallel()
 	ctx, _ := testJava(t, `
 		java_library {
 			name: "foo",
@@ -44,6 +45,7 @@ func TestNoPlugin(t *testing.T) {
 }
 
 func TestPlugin(t *testing.T) {
+	t.Parallel()
 	ctx, _ := testJava(t, `
 		java_library {
 			name: "foo",
@@ -83,6 +85,7 @@ func TestPlugin(t *testing.T) {
 }
 
 func TestPluginGeneratesApi(t *testing.T) {
+	t.Parallel()
 	ctx, _ := testJava(t, `
 		java_library {
 			name: "foo",