twister: DeviceHandler improve DUT selection

Improve DUT selection at DeviceHandler: for each DUT it counts
how many test instances have been failed on it during the current
twister execution, so the next available DUT will be chosen
ordering the eligible DUTs by less failures occured so far.

The new selection mechanism should increase chances to retry failed
tests on different DUTs, for instance to resolve ploblems when some
DUTs have connectivity or HW issues slowing down test plan execution,
or even block the execution when only one test suite runs whereas
the same first DUT candidate in the list is not working and others
were not chosen.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>