Add VBUS current check for type-C charging test

1. add poll_pd_state for plankton class. The state transition (between
sink and source) will take a short time. If we want to make sure test
checking in stable state, we should poll it.

2. add VBUS current check (same as the metric of factory test). Check
current is around 3A in charging 5V, and others current is over 0A.

3. make plankton object as local since it is only used inside run_once.

  test_that --fast -b typec_host_board due_ip_address \

Change-Id: I9a544b3a0e96a35df916069619895172612333e5
Reviewed-by: Wai-Hong Tam <>
Commit-Queue: Pin-chih Lin <>
Tested-by: Pin-chih Lin <>
2 files changed