flashall.bat: handle dfu errors correctly during flash
flashall.bat: handle dfu errors correctly during flash

Some flashing commands are piped and checked with %errorlevel% variable.
This will only check errors from the right command (and won't check for
potential dfu-util errors).
This patch calls dfu command and save its errorlevel in a temp file, then
pipe the dfu command as usual.

Tracked-On: EDISON-2324
Signed-off-by: Rodriguez Fabien <9977a78a23707868610ccbb15bf27c4cd752553a@intel.com>

oesile/meta-intel-edison,oesile/meta-intel-edison,oesile/meta-intel-edison,oesile/meta-intel-edison,htot/meta-intel-edison,oesile/meta-intel-edison,htot/meta-intel-edison,oesile/meta-intel-edison,htot/meta-intel-edison,oesile/meta-intel-edison,htot/meta-intel-edison,oesile/meta-intel-edison,htot/meta-intel-edison