Add debug-level message on error for Jaeger Exporter

[jpkrohling]

Signed-off-by: Juraci Paixão Kröhling juraci@kroehling.de

Important (read before submitting)

Description:
When trying to get the OpenTelemetry Collector to work with Jaeger, it's currently not easy to determine whether a batch has failed to be sent to Jaeger, as there are no logs recorded anywhere.
This PR adds a debug-level message with the error. Users doing an initial setup, or having problems, can enable debug logging and will be able to identify what's wrong.

Example output:

2020-10-15T14:35:55.203+0200	DEBUG	jaegerexporter/exporter.go:95	failed to push trace data to Jaeger	{"component_kind": "exporter", "component_type": "jaeger", "component_name": "jaeger/auth", "error": "rpc error: code = Unknown desc = authentication didn't succeed"}

Link to tracking Issue: n/a

Testing: manual test

Documentation: n/a

[jpkrohling]

PR updated.

[codecov]

Codecov Report

Merging #1964 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1964      +/-   ##
==========================================
+ Coverage   91.48%   91.49%   +0.01%     
==========================================
  Files         280      280              
  Lines       16500    16502       +2     
==========================================
+ Hits        15095    15099       +4     
+ Misses        974      973       -1     
+ Partials      431      430       -1     

Impacted Files	Coverage Δ
exporter/jaegerexporter/exporter.go	88.23% <100.00%> (+0.73%)	⬆️
exporter/jaegerexporter/factory.go	92.30% <100.00%> (ø)
translator/internaldata/resource_to_oc.go	94.52% <0.00%> (+2.73%)	⬆️

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[jpkrohling]

Those are unrelated, right?

# github.com/open-telemetry/opentelemetry-collector-contrib/testbed/datasenders
datasenders/carbon.go:32:2: undefined: testbed.DataSenderBase
datasenders/sapm.go:31:2: undefined: testbed.DataSenderBase
datasenders/signalfx.go:31:2: undefined: testbed.DataSenderBase
?   	github.com/open-telemetry/opentelemetry-collector-contrib/testbed/datareceivers	[no test files]
FAIL	github.com/open-telemetry/opentelemetry-collector-contrib/testbed/stabilitytests [build failed]
FAIL	github.com/open-telemetry/opentelemetry-collector-contrib/testbed/tests [build failed]
make[1]: *** [Makefile.Common:49: test] Error 2
make[1]: Leaving directory '/tmp/opentelemetry-collector-contrib'
make: *** [Makefile:313: check-contrib] Error 2

[jpkrohling]

Rebased, hopefully the contrib-test is fixed by now?