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/android/rule_builder_test.go b/android/rule_builder_test.go
index c41b067..d205a5b 100644
--- a/android/rule_builder_test.go
+++ b/android/rule_builder_test.go
@@ -264,6 +264,7 @@
 }
 
 func TestRuleBuilder(t *testing.T) {
+	t.Parallel()
 	fs := map[string][]byte{
 		"dep_fixer":  nil,
 		"input":      nil,
@@ -455,6 +456,7 @@
 }
 
 func TestRuleBuilder_Build(t *testing.T) {
+	t.Parallel()
 	fs := map[string][]byte{
 		"bar": nil,
 		"cp":  nil,
@@ -546,6 +548,7 @@
 }
 
 func Test_ninjaEscapeExceptForSpans(t *testing.T) {
+	t.Parallel()
 	type args struct {
 		s     string
 		spans [][2]int