[WORKER][ADMIN_API]: Add device diagnostics check

After a device is built run a diagnostics check on the device.
1. The pool manager will send a DIAGNOSTICS message to the device after build
2. The worker will:
  a. Connect test google
  b. Connect test all gearman servers
3. If google connect test fails device is failed
4. If > 1/3rd gearman servers connect fails the device is failed
5. Failed devices are deleted and a FAIL response for that build is returned

Change-Id: Iaac8fabeabb4136451407164e396f784eabaf887