acloud: implement autoconnect for create commands.

This involves setting up ssh tunnels for adb/vnc.

Bug: 116681363
Test: atest acloud_test
out/host/linux-x86/bin/acloud create

Change-Id: I910b1ab92d0bd781816e03c01b4b698b875e9c8f
diff --git a/errors.py b/errors.py
index 6a5cb54..ceaa015 100644
--- a/errors.py
+++ b/errors.py
@@ -102,3 +102,7 @@
 
 class LaunchCVDFail(CreateError):
     """Cuttlefish AVD launch failed."""
+
+
+class NoExecuteCmd(CreateError):
+    """Can't find execute bin command."""