OkHttpTransportTest.serverChecksInboundMetadataSize is flaky

[creamsoup]

https://travis-ci.org/grpc/grpc-java/jobs/490335355 (java8 travis)

io.grpc.okhttp.OkHttpTransportTest > serverChecksInboundMetadataSize FAILED
    java.lang.AssertionError: Status code was not expected: Status{code=UNAVAILABLE, description=End of stream or IOException, cause=null}

[creamsoup]

from @carl-mastrangelo

Noticed here: https://travis-ci.org/grpc/grpc-java/jobs/492953187

> Task :grpc-okhttp:test
io.grpc.okhttp.OkHttpTransportTest > serverChecksInboundMetadataSize FAILED
    java.lang.AssertionError: Status code was not expected: Status{code=UNAVAILABLE, description=End of stream or IOException, cause=null}

[creamsoup]

https://travis-ci.org/grpc/grpc-java/jobs/516435873

io.grpc.okhttp.OkHttpTransportTest > serverChecksInboundMetadataSize FAILED
    java.lang.AssertionError: Status code was not expected: Status{code=UNAVAILABLE, description=End of stream or IOException, cause=null}

[voidzcy]

https://travis-ci.org/grpc/grpc-java/jobs/551896217

io.grpc.okhttp.OkHttpTransportTest > serverChecksInboundMetadataSize FAILED
    java.lang.AssertionError: Status code was not expected: Status{code=UNAVAILABLE, description=End of stream or IOException, cause=null}

[creamsoup]

https://travis-ci.org/grpc/grpc-java/jobs/590538160

io.grpc.okhttp.OkHttpTransportTest > serverChecksInboundMetadataSize FAILED
    java.lang.AssertionError: Status code was not expected: Status{code=UNAVAILABLE, description=End of stream or IOException, cause=null}

[creamsoup]

https://travis-ci.org/grpc/grpc-java/jobs/591599599