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/sdk/exports_test.go b/sdk/exports_test.go
index aa1200f..173ccb9 100644
--- a/sdk/exports_test.go
+++ b/sdk/exports_test.go
@@ -20,6 +20,7 @@
 
 // Ensure that module_exports generates a module_exports_snapshot module.
 func TestModuleExportsSnapshot(t *testing.T) {
+	t.Parallel()
 	packageBp := `
 		module_exports {
 			name: "myexports",