Avoid calling handleClientConnection if initializeClientConnection fails

[djones6]

Description

This is a follow-on to #219, which split out the socket accept from the protocol initialization for SSL connections, in order to perform the latter on a separate thread.

In the case where the socket initialization fails, such as with an SSL handshake error, following #219 we would log the error but then attempt to handle the client connection anyway, resulting in unnecessary work and further errors.

This PR moves the do/catch logic for initializeClientConnection so that we only try to call handleClientConnection if the former was successful.

I also updated the log messages to document the source of a connection when it fails initialization.

Motivation and Context

Avoids unnecessary attempts to handle a connection for which the SSL initialization has failed, and reporting of further errors as a consequence.

How Has This Been Tested?

I have run the Kitura-net tests and they are passing. Note that there is an intermittent test failure exposed by the test intrduced in #219 - which intentionally generates a bad connection to an SSL listener - which will be resolved by Kitura/BlueSSLService#42.

Checklist:

• I have submitted a CLA form
• If applicable, I have updated the documentation accordingly.
• If applicable, I have added tests to cover my changes.

[codecov-io]

Codecov Report

Merging #221 into master will decrease coverage by 0.27%.
The diff coverage is 70%.

@@            Coverage Diff             @@
##           master     #221      +/-   ##
==========================================
- Coverage   74.02%   73.75%   -0.28%     
==========================================
  Files          31       31              
  Lines        4146     4145       -1     
==========================================
- Hits         3069     3057      -12     
- Misses       1077     1088      +11

Flag	Coverage Δ
#CHTTPParser	56.11% <ø> (ø)	⬆️
#KituraNet	73.75% <70%> (-0.28%)	⬇️

Impacted Files	Coverage Δ
Sources/KituraNet/HTTP/HTTPServer.swift	79.09% <70%> (-1.81%)	⬇️
Sources/KituraNet/IncomingSocketManager.swift	85.45% <0%> (-5.46%)	⬇️
...ces/KituraNet/Server/ServerLifecycleListener.swift	79.16% <0%> (-4.17%)	⬇️
Sources/KituraNet/IncomingSocketHandler.swift	76.99% <0%> (-1.88%)	⬇️

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[djones6]

I'm accepting the apparent reduction in coverage - this is really because of a fix I added to BlueSSLService which no longer (erroneously) triggers an error handling path. Raised #222 for a proper test for this path.

[tunniclm]

lgtm