udevadm-control: parse all args in advance

udevadm-control: parse all args in advance

This is mostly just refactoring to make the code more manageable and
extendable. It doesn't introduce any semantic changes, but it
"optimizes" the communication with udevd a bit:
* If an option is used multiple times, only one command will be sent. If
  the option takes a value, the value of the final appearance of the
  option is used. The only exception is --property, which is additive by
  nature.
* Options --start-exec-queue and --stop-exec-queue are handled together.
  Only one of START_QUEUE/STOP_QUEUE commands will be sent to udevd even
  if both options appear on the command line.