check-wda can't use new ip address

[vdelendik]

in case we change ip address of the iOS device our check-wda.sh continue to execute verification using old value and restart WDA constantly...

Good way to repro:

1. start everything correctly
2. disable wi-fi
3. restart iOS container zebrunner-farm restart udid
   -> WDA tries to start using localhost which is wrong
4. enable wi-fi again
   -> wda is started correctly, env file is populated with valid data but check-wda.sh continue to use localhost...

So we have to reload WDA_HOST and MJPEG_PORT at run-time before validation...
P.S. Think about zero file size check to avoid forcibly restart during restart

[vdelendik]

done. please follow above scenario to test that new WDA_HOST ip is propagated correctly

[dhreben]

Verified.