Reintroduce SEQUENCEFILE writer tests

The sequence writer test had an issue with zlib on certain cluster machines, making
this a flaky test. This has passed several times locally and in private builds. This
re-enables the test because the failures could not be produced in private builds.

Change-Id: I0aeea3a2d000e711e5a84427a7b40592e1eef75b
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5077
Reviewed-by: Victor Bittorf <victor.bittorf@cloudera.com>
Tested-by: jenkins