Guard socket read(), write(), close() race conditions and use SSL tests

[na-gupta]

Description

• Add state guards for IncomingSocketHandler read() write() and close() functions
• Make sure we don't close sockets while they're being used or try to use them after they're closed
• Make most unit tests use SSLService as it surfaces race condition problems whereas Socket mostly ignores them

Motivation and Context

Kitura/Kitura#959
Kitura/Kitura#962

How Has This Been Tested?

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]

Current coverage is 83.56% (diff: 67.74%)

Merging #169 into master will decrease coverage by 0.08%

@@             master       #169   diff @@
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  Files            27         27          
  Lines          2348       2373    +25   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
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+ Hits           1964       1983    +19   
- Misses          384        390     +6   
  Partials          0          0          

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