acloud: autoconnect default value set as vnc

revise --autoconnect default value from True to 'vnc' that logic is more clear.

BUG: 147080194
Test: acloud-dev create
      acloud-dev create --autoconnect vnc
      acloud-dev create --autoconnect adb
Change-Id: I3168cd6c12a228c5cae2a27dbc36d5e072c3623c
3 files changed