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/symbol_inject/elf_test.go b/symbol_inject/elf_test.go
index aceee44..316c69a 100644
--- a/symbol_inject/elf_test.go
+++ b/symbol_inject/elf_test.go
@@ -20,6 +20,7 @@
 )
 
 func TestElfSymbolTable(t *testing.T) {
+	t.Parallel()
 	testCases := []struct {
 		file         *mockElfFile
 		symbol       string