cmd/query: init tracer config from env

[holycheater]

Which problem is this PR solving?

Resolves #1044

Getting a lot of these errors in jaeger-query docker image:
{"level":"error","ts":1568465347.7179556,"caller":"zap/logger.go:33","msg":"error when flushing the buffer: write udp 127.0.0.1:59514->127.0.0.1:6831: write: connection refused","stacktrace":"github.com/jaegertracing/jaeger/vendor/github.com/uber/jaeger-client-go/log/zap.(*Logger).Error\n\t/home/travis/gopath/src/github.com/jaegertracing/jaeger/vendor/github.com/uber/jaeger-client-go/log/zap/logger.go:33\ngitpro.ttaallkk.top/jaegertracing/jaeger/vendor/github.com/uber/jaeger-client-go.(*remoteReporter).processQueue.func1\n\t/home/travis/gopath/src/github.com/jaegertracing/jaeger/vendor/github.com/uber/jaeger-client-go/reporter.go:257\ngitpro.ttaallkk.top/jaegertracing/jaeger/vendor/github.com/uber/jaeger-client-go.(*remoteReporter).processQueue\n\t/home/travis/gopath/src/github.com/jaegertracing/jaeger/vendor/github.com/uber/jaeger-client-go/reporter.go:267"}

Short description of the changes

Using jaeger-client-go FromEnv configuration

[yurishkuro]

Unfortunately, this is not backwards compatible. This really needs to be fixed in the client, so that FromEnv could be called on an already populated config as a for of override.

[holycheater]

Making changes to client for this single application seems like an overkill
I've made changes in tracer config initialization, should be backwards-compatible now

[codecov]

Codecov Report

Merging #1800 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1800      +/-   ##
==========================================
- Coverage   98.21%   98.17%   -0.05%     
==========================================
  Files         195      195              
  Lines        9602     9602              
==========================================
- Hits         9431     9427       -4     
- Misses        134      137       +3     
- Partials       37       38       +1

Impacted Files	Coverage Δ
cmd/query/app/static_handler.go	83.33% <0%> (-3.51%)	⬇️

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[yurishkuro]

Sorry, I was probably unclear. I don't think this repository needs to solve it by re-implementing env var lookup. The issue is in the jaeger-client-go: jaegertracing/jaeger-client-go#430

[pavolloffay]

Done in #1919