Avoid duplicate exceptions on VM Service Mock failure (#10197)
Avoid duplicate exceptions on VM Service Mock failure (#10197)

On failure to configure a mock VM service, we get a useful exception in
setUpAll(). This change prevents an additional failure in tearDownAll()
that provides no additional useful diagnostic info.
flutter/flutter,flutter/flutter,flutter/flutter,turnidge/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,turnidge/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,turnidge/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,turnidge/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,turnidge/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter