vc: set store RunVMStoragePath for ut

Otherwise we fail ut on failures like:

=== RUN   TestCloudHypervisorCleanupVM
--- FAIL: TestCloudHypervisorCleanupVM (0.00s)
    clh_test.go:191: cloudHypervisor.cleanupVM() expected error != open /run/vc/vm: permission denied
    clh_test.go:200: Unexpected error = stat /run/vc/vm/cleanVMID: permission denied
=== RUN   TestClhCreateSandbox
--- PASS: TestClhCreateSandbox (0.00s)
=== RUN   TestClooudHypervisorStartSandbox
time="2019-12-25T00:48:47-08:00" level=error msg="trace called before context set" source=virtcontainers subsystem=cloudHypervisor type=bug
--- FAIL: TestClooudHypervisorStartSandbox (0.00s)
        Error Trace:    clh_test.go:266
        Error:          Received unexpected error:
                        mkdir /run/vc/vm: permission denied

Signed-off-by: Peng Tao <bergwolf@hyper.sh>

virtcontainers/virtcontainers_test.go

@@ -57,21 +57,28 @@ var testVirtiofsdPath = ""
 var testHyperstartCtlSocket = ""
 var testHyperstartTtySocket = ""
 
+var savedRunVMStoragePathFunc func() string
+
 // cleanUp Removes any stale sandbox/container state that can affect
 // the next test to run.
 func cleanUp() {
 	globalSandboxList.removeSandbox(testSandboxID)
 	store.DeleteAll()
 	os.RemoveAll(testDir)
-	os.MkdirAll(testDir, store.DirMode)
 	store.VCStorePrefix = ""
+	store.RunVMStoragePath = savedRunVMStoragePathFunc
 
 	setup()
 }
 
 func setup() {
-	os.Mkdir(filepath.Join(testDir, testBundle), store.DirMode)
 	store.VCStorePrefix = testDir
+	savedRunVMStoragePathFunc = store.RunVMStoragePath
+	store.RunVMStoragePath = func() string {
+		return filepath.Join("testDir", "vm")
+	}
+	os.MkdirAll(store.RunVMStoragePath(), store.DirMode)
+	os.MkdirAll(filepath.Join(testDir, testBundle), store.DirMode)
 
 	for _, filename := range []string{testQemuKernelPath, testQemuInitrdPath, testQemuImagePath, testQemuPath} {
 		_, err := os.Create(filename)