NIFI-8304 Replaced HttpsURLConnection with OkHttp in TestListenHTTP

[exceptionfactory]

Description of PR

NIFI-8304-4 Replaces HttpsURLConnection with OkHttpClient in TestListenHTTP in an effort to provide a more reliable approach to making requests over HTTP and HTTPS. Each test method creates a new instance of OkHttpClient and avoids reusing connections. TestListenHTTP did not call disconnect() on HttpsURLConnection and could have failed to close the connection output stream in certain conditions. Use of OkHttpClient also includes setting a 10 second call timeout to avoid extended waits for failing requests.

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