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

cmd/host_bionic_inject/host_bionic_inject_test.go

@@ -100,6 +100,7 @@ func linkerOffset() []elf.Symbol {
 }
 
 func TestCheckLinker(t *testing.T) {
+	t.Parallel()
 	cases := []struct {
 		name   string
 		err    error