RFR: 8223714: HTTPSetAuthenticatorTest could be made more resilient

[Jaikiran Pai]

Can I please get a review and a sponsor for a patch for
https://bugs.openjdk.java.net/browse/JDK-8223714?

The patch is available as a webrev at
http://cr.openjdk.java.net/~jpai/webrev/8223714/1/webrev/

This issue and the patch relates solely to a test infrastructure class -
HTTPTestServer and touches no main source code. The patch involves the
following:

- A straightforward fix in the readLine method which prevents the
java.lang.StringIndexOutOfBoundsException reported in that JIRA.

- Additional changes to the run() method of the server to make the
connection handling and processing of this (test) server a bit more robust.

    - The run method now accepts a connection and if while processing
the client request on that connection, runs into a IOException, then
closes the client connection and then continues to accept any subsequent
connections (this wasn't the case previously, where the server would
just abort and no longer accept any more connections).

    - Any non IOException(s) are logged and the server goes on to accept
any subsequent requests.

    - Whether or not to accept any more connections is now handled by
the "stop" flag which gets set when the server stop is requested.

    - Any failure to "accept()" a connection stops the server from
accepting any more requests. This is also now clearly logged as a log
message.

    - The bulk of the parsing and processing of the client request has
been moved out of the run() method into a new private
processRequestAndWaitToComplete method, for better code clarity.

I haven't been able to reproduce the original exception reported in the
JBS issue, before doing any of these changes. However, I have run the
existing HTTPSetAuthenticatorTest, both before and after these changes
and it has worked fine. Given that the changes are only in the test
infrastructure, supporting the test cases, I haven't added any new jtreg
test, to test these changes.

-Jaikiran