fail fast if no suitable devices found

[jupe]

https://github.com/DeviceFarmer/stf/blob/489ba0427e5dd8178c29f4bdd836bfee7d199cce/lib/wire/wire.proto#L365

enum DeviceStatus {
  OFFLINE = 1;
  UNAUTHORIZED = 2;
  ONLINE = 3;
  CONNECTING = 4;
  AUTHORIZING = 5;
}

if device is anything else than online - it's filtered away and fail fast if no any devices left

[coveralls]

Pull Request Test Coverage Report for Build 10210294477

Details

• 11 of 12 (91.67%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 84.222%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
stf_appium_client/StfClient.py	11	12	91.67%

Totals
Change from base Build 8417470659:	0.1%
Covered Lines:	379
Relevant Lines:	450

---

💛 - Coveralls