async code will cause dead lock with xunit

[frank-dong-ms-zz]

xunit/xunit#864
xunit/xunit#1935

Calling .Wait() causes deadlocks.
Calling .Result causes deadlocks.
Calling .GetAwaiter().GetResult() causes deadlocks.

we need to fix the way we use in async to prevent dead lock with xunit

[frank-dong-ms-zz]

Introduced threading analyzer and fix hanging:
#4790
#4791
#4792
#4793
#4794