test: add SSL test

[jeblair]

This adds a simple SSL test along with the framework for running the test Zookeeper in a mode where it listens on both SSL and non-SSL ports.

This is based on earlier work in #619.

[jeffwidman]

nudge @jeblair

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (aa21989) 96.62% compared to head (a05f8ed) 96.65%. Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #620      +/-   ##
==========================================
+ Coverage   96.62%   96.65%   +0.02%     
==========================================
  Files          27       27              
  Lines        3557     3557              
==========================================
+ Hits         3437     3438       +1     
+ Misses        120      119       -1     

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[StephenSorriaux]

I rebased this PR but it is not working because ZK is expecting a keystore and a truststore (java stuff) instead of .pem files. Will try to get this working soon and add some "cert auto generation".

[StephenSorriaux]

@jeffwidman @ceache @jeblair this one is finalized, would love a review to get it merged.

[jeblair]

Thanks for updating this. ZK can use a pem file that is just a concatenation of the cert and key as its "keystore" without any special jks functionality. But since that seems to have bitrotted in this PR somehow, doing all the actual jks stuff is probably going to be more robust in the long run. :)

[StephenSorriaux]

Thank you again for the PR @jeblair and thank you for the updated information. I remember using a product that would "weirdly" accept this kind of .pem files as a "keystore" and you are certainly right that it was ZK. My comment about the reason why the tests were failing was probably wrong.