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

rust/coverage_test.go

@@ -23,6 +23,7 @@ import (
 
 // Test that coverage flags are being correctly generated.
 func TestCoverageFlags(t *testing.T) {
+	t.Parallel()
 	ctx := testRustCov(t, `
 		rust_library {
 			name: "libfoo_cov",
@@ -98,6 +99,7 @@ func TestCoverageFlags(t *testing.T) {
 
 // Test coverage files are included correctly
 func TestCoverageZip(t *testing.T) {
+	t.Parallel()
 	ctx := testRustCov(t, `
 		rust_library {
 			name: "libfoo",
@@ -174,6 +176,7 @@ func TestCoverageZip(t *testing.T) {
 }
 
 func TestCoverageDeps(t *testing.T) {
+	t.Parallel()
 	ctx := testRustCov(t, `
 		rust_binary {
 			name: "fizz",