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/cmd/path_interposer/main_test.go b/cmd/path_interposer/main_test.go
index c89d623..3f1a5e1 100644
--- a/cmd/path_interposer/main_test.go
+++ b/cmd/path_interposer/main_test.go
@@ -61,6 +61,7 @@
 }
 
 func TestInterposer(t *testing.T) {
+	t.Parallel()
 	interposer := setup(t)
 
 	logConfig := func(name string) paths.PathConfig {
@@ -180,6 +181,7 @@
 }
 
 func TestMissingPath(t *testing.T) {
+	t.Parallel()
 	interposer := setup(t)
 	err := os.Remove(interposer + "_origpath")
 	if err != nil {