Add logs for slow HTTP requests dumping the profile

There are several endpoints in WebUI that can dump a query profile: /query_profile, /query_profile_encoded, /query_profile_plain_text, /query_profile_json

The HTTP handler thread goes into ImpalaServer::GetRuntimeProfileOutput() which acquires lock of the ClientRequestState. This could blocks client requests in fetching query results. We should add warning logs when such HTTP requests run slow (e.g. when the profile is too large to download in a short time). IP address and other info of such requests should also be logged.

Related codes:
https://github.com/apache/impala/blob/f620e5d5c0bbdb0fd97bac31c7b7439cd13c6d08/be/src/service/impala-server.cc#L736
https://github.com/apache/impala/blob/f620e5d5c0bbdb0fd97bac31c7b7439cd13c6d08/be/src/service/impala-beeswax-server.cc#L601
https://github.com/apache/impala/blob/f620e5d5c0bbdb0fd97bac31c7b7439cd13c6d08/be/src/service/impala-hs2-server.cc#L207