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/genrule/genrule_test.go b/genrule/genrule_test.go
index 4b36600..66bb221 100644
--- a/genrule/genrule_test.go
+++ b/genrule/genrule_test.go
@@ -125,6 +125,7 @@
 }
 
 func TestGenruleCmd(t *testing.T) {
+	t.Parallel()
 	testcases := []struct {
 		name string
 		prop string
@@ -503,6 +504,7 @@
 }
 
 func TestGenruleHashInputs(t *testing.T) {
+	t.Parallel()
 
 	// The basic idea here is to verify that the sbox command (which is
 	// in the Command field of the generate rule) contains a hash of the
@@ -590,6 +592,7 @@
 }
 
 func TestGenSrcs(t *testing.T) {
+	t.Parallel()
 	testcases := []struct {
 		name string
 		prop string
@@ -682,6 +685,7 @@
 }
 
 func TestGenruleDefaults(t *testing.T) {
+	t.Parallel()
 	bp := `
 				genrule_defaults {
 					name: "gen_defaults1",