ProvisionerDockerLocalStoreTest.MissingLayer is flaky.

../../src/tests/containerizer/provisioner_docker_tests.cpp:284
(imageInfo).failure(): Collect failed: Subprocess 'tar, tar, -x, -f, /tmp/nQt3Eu/store/staging/D1LuiF/123/layer.tar, -C, /tmp/nQt3Eu/store/staging/D1LuiF/123/rootfs' failed: tar: This does not look like a tar archive
tar: Exiting with failure status due to previous errors

[ RUN      ] ProvisionerDockerLocalStoreTest.MissingLayer
sh: 1: hadoop: not found
I0702 07:48:37.257685 13822 fetcher.cpp:69] Skipping URI fetcher plugin 'hadoop' as it could not be created: Failed to create HDFS client: Hadoop client is not available, exit status: 32512
I0702 07:48:37.257894 13822 image_tar_puller.cpp:128] Creating image tar puller with docker registry '/tmp/nQt3Eu/images'
I0702 07:48:37.258908  2602 metadata_manager.cpp:179] Looking for image 'abc'
I0702 07:48:37.259110  2603 image_tar_puller.cpp:210] Untarring image 'abc' from '/tmp/nQt3Eu/images/abc.tar' to '/tmp/nQt3Eu/store/staging/D1LuiF'
I0702 07:48:37.358192  2602 image_tar_puller.cpp:231] The repositories JSON file for image 'abc' is '{"abc":{"latest":"456"}}'
I0702 07:48:37.358373  2602 image_tar_puller.cpp:375] Extracting layer tar ball '/tmp/nQt3Eu/store/staging/D1LuiF/123/layer.tar to rootfs '/tmp/nQt3Eu/store/staging/D1LuiF/123/rootfs'
I0702 07:48:37.360628  2602 image_tar_puller.cpp:375] Extracting layer tar ball '/tmp/nQt3Eu/store/staging/D1LuiF/456/layer.tar to rootfs '/tmp/nQt3Eu/store/staging/D1LuiF/456/rootfs'
../../src/tests/containerizer/provisioner_docker_tests.cpp:284: Failure
(imageInfo).failure(): Collect failed: Subprocess 'tar, tar, -x, -f, /tmp/nQt3Eu/store/staging/D1LuiF/123/layer.tar, -C, /tmp/nQt3Eu/store/staging/D1LuiF/123/rootfs' failed: tar: This does not look like a tar archive
tar: Exiting with failure status due to previous errors

[  FAILED  ] ProvisionerDockerLocalStoreTest.MissingLayer (302 ms)