Support the TCP/UNIX parameter for server/client

[hwchiu]

• For Server, use the -tcp=0.0.0.0:50051 or -unix=/tmp/a.sock to listen
• For Client, use the -server=0.0.0.0:50051 or -server=unix:///tmp/a.sock to connect
• Check the OVS/Docker Environment before local testing
  • Make test
• Modify the README
• For Server, Fix the signal problem

[codecov]

Codecov Report

Merging #24 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #24   +/-   ##
=======================================
  Coverage   85.03%   85.03%           
=======================================
  Files           5        5           
  Lines         127      127           
=======================================
  Hits          108      108           
  Misses         12       12           
  Partials        7        7

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