Fix race condition in e2e SmokeTest

[kevinearls]

The smoketest can fail here if the first span has not been flushed by the time the test does the http get.

https://github.com/jaegertracing/jaeger-operator/blob/master/test/e2e/smoketest.go#L46-L52

[pavolloffay]

The whole block is in wait.Pool so if the spans is not there the request to query service is repeated.

[kevinearls]

@pavolloffay I think the problem is that if you don't find the span you're looking for on the first try, this line returns an error, so the test terminates. https://github.com/jaegertracing/jaeger-operator/blob/master/test/e2e/smoketest.go#L50

[pavolloffay]

I see that one should return nil