esx: Add automatic question handling

esx: Add automatic question handling

Questions can block tasks, to handle them automatically the driver can answers
them with the default answer. The auto_answer query parameter allows to enable
this automatic question handling.

* src/esx/README: add a detailed explanation for automatic question handling
* src/esx/esx_driver.c: add automatic question handling for all task related
  driver functions
* src/esx/esx_util.[ch]: add handling for the auto_answer query parameter
* src/esx/esx_vi.[ch], src/esx/esx_vi_methods.[ch], src/esx/esx_vi_types.[ch]:
  add new VI API methods and types and additional helper functions for
  automatic question handling