acloud: Mkcert install failed

Mkcert install process fail caused by mkcert directory existed.
Add a check to solve the problem

Bug: 195474146
Test: acloud-dev create --autoconnect webrtc --local-image
--local-instance

Change-Id: If84b43b31e6037d512a4495af2ecae2ceccb0cd5
diff --git a/setup/host_setup_runner.py b/setup/host_setup_runner.py
index 2952f12..e272d88 100644
--- a/setup/host_setup_runner.py
+++ b/setup/host_setup_runner.py
@@ -198,7 +198,8 @@
                                       "enter to exit: " % cmd):
             sys.exit(constants.EXIT_BY_USER)
 
-        os.mkdir(_MKCERT_INSTALL_PATH)
+        if not os.path.isdir(_MKCERT_INSTALL_PATH):
+            os.mkdir(_MKCERT_INSTALL_PATH)
         setup_common.CheckCmdOutput(cmd, shell=True)
         utils.SetExecutable(os.path.join(_MKCERT_INSTALL_PATH, "mkcert"))
         utils.CheckOutput(_MKCERT_CAROOT_CMD, shell=True)