Improve debug logging
Improve debug logging

Summary:
This is done to simplify debugging of crashes, which can happen because of corrupted strings presence in application resources. I've already seen several issues about WDA crashes due to an unexpected non-UTF-8 character in application resources.
We could also ignore such errors and replace/not include damaged strings while parsing UI tree.
Closes https://github.com/facebook/WebDriverAgent/pull/520

Differential Revision: D4763037

Pulled By: marekcirkos

fbshipit-source-id: ee3c18f38d1cf060b5837d9800f901d4b87e973c

b1ueshad0w/WebDriverAgent,b1ueshad0w/WebDriverAgent,Gogle/WebDriverAgent,b1ueshad0w/WebDriverAgent,Gogle/WebDriverAgent,PiranhaTeam/WebDriverAgent,qa-dev/WebDriverAgent,Gogle/WebDriverAgent,PiranhaTeam/WebDriverAgent,ymin/WebDriverAgent,PiranhaTeam/WebDriverAgent,qa-dev/WebDriverAgent,PiranhaTeam/WebDriverAgent,Gogle/WebDriverAgent,b1ueshad0w/WebDriverAgent,ymin/WebDriverAgent,qa-dev/WebDriverAgent,ymin/WebDriverAgent,qa-dev/WebDriverAgent,PiranhaTeam/WebDriverAgent,ymin/WebDriverAgent