Add ipv6 support

[alvassin]

Added ability to report spans to ipv6 only hosts using:

• config local_agent.reporting_host_use_ipv6 option
• JAEGER_AGENT_HOST_USE_IPV6 environment variable.
• if none of above options are not specified, jaeger client checks if host behind reporting_host is ipv6 only.

Resolves #337

[yurishkuro]

Since you're automatically determining if the address is IPv6-only, what is the value proposition of this new property? To put it differently, what is the downside of not exposing it and always handling the v4/v6 automatically?

[alvassin]

Resonable. Added _create_socket method to TUDPTransport class, that can be overriden, removed config options.

Also, socket.set_blocking() requires boolean, so i removed the following block (perhaps there is a reason to keep it):

if blocking:
    blocking = 1
else:
    blocking = 0

[alvassin]

Added tests

[codecov]

Codecov Report

Merging #339 (bb59e4e) into master (1341016) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #339      +/-   ##
==========================================
+ Coverage   95.30%   95.32%   +0.01%     
==========================================
  Files          25       25              
  Lines        2046     2053       +7     
  Branches      275      275              
==========================================
+ Hits         1950     1957       +7     
  Misses         61       61              
  Partials       35       35              

Impacted Files	Coverage Δ
jaeger_client/TUDPTransport.py	100.00% <100.00%> (ø)

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