fix: zipkin-exporter: don't export after shutdown

[Flarna]

Which problem is this PR solving?

According to spec and exporter should return FailedNotRetryable error
after shutdown was called.

see https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/sdk-tracing.md#shutdown-1

After the call to Shutdown subsequent calls to Export are not allowed and should return FailedNotRetryable error.

Short description of the changes

Remember that shutdown() was called and if yes immediate call callback with error.

[codecov-io]

Codecov Report

Merging #526 into master will increase coverage by 47.31%.
The diff coverage is 92.3%.

@@             Coverage Diff             @@
##           master     #526       +/-   ##
===========================================
+ Coverage    49.2%   96.52%   +47.31%     
===========================================
  Files          47      132       +85     
  Lines        1392     6361     +4969     
  Branches      143      566      +423     
===========================================
+ Hits          685     6140     +5455     
+ Misses        707      221      -486

Impacted Files	Coverage Δ
.../opentelemetry-exporter-zipkin/test/zipkin.test.ts	100% <100%> (ø)
...ckages/opentelemetry-exporter-zipkin/src/zipkin.ts	98.43% <85.71%> (ø)
...ckages/opentelemetry-core/src/common/NoopLogger.ts	33.33% <0%> (-16.67%)	⬇️
...metry-core/src/trace/instrumentation/BasePlugin.ts	80.55% <0%> (-5.56%)	⬇️
...ges/opentelemetry-core/src/common/ConsoleLogger.ts	93.33% <0%> (-0.79%)	⬇️
...telemetry-core/src/context/propagation/B3Format.ts	96.42% <0%> (-0.72%)	⬇️
...core/src/context/propagation/BinaryTraceContext.ts	97.5% <0%> (-0.54%)	⬇️
...core/src/context/propagation/NoopHttpTextFormat.ts	100% <0%> (ø)	⬆️
.../opentelemetry-core/src/trace/spancontext-utils.ts	100% <0%> (ø)	⬆️
...ages/opentelemetry-core/src/internal/validators.ts	100% <0%> (ø)	⬆️
... and 125 more

[mayurkale22]

Looks like same thing needs to be implemented for Jaeger exporter.

[obecny]

lgtm, one comment

[Flarna]

Seems we have an issue with the just released node type definitions (DefinitelyTyped/DefinitelyTyped#40118):

src/http.ts:343:15 - error TS2345: Argument of type 'UrlWithStringQuery | null' is not assignable to parameter of type 'RequestOptions | (RequestOptions & Partial<UrlWithParsedQuery>) | null'.
  Type 'UrlWithStringQuery' is not assignable to type 'RequestOptions | (RequestOptions & Partial<UrlWithParsedQuery>) | null'.
    Type 'UrlWithStringQuery' is not assignable to type 'RequestOptions & Partial<UrlWithParsedQuery>'.
      Type 'UrlWithStringQuery' is not assignable to type 'RequestOptions'.
        Types of property 'protocol' are incompatible.
          Type 'string | null' is not assignable to type 'string | undefined'.
            Type 'null' is not assignable to type 'string | undefined'.