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/rust/clippy_test.go b/rust/clippy_test.go
index 7815aab..786dc15 100644
--- a/rust/clippy_test.go
+++ b/rust/clippy_test.go
@@ -21,6 +21,7 @@
 )
 
 func TestClippy(t *testing.T) {
+	t.Parallel()
 
 	bp := `
 		// foo uses the default value of clippy_lints