Fix compressed text reader/write to use SNAPPY_BLOCKED instead of SNAPPY.

Since this is a hadoop codec, we always need to use SNAPPY_BLOCKED.

Change-Id: I8635c2473036b4a9bd1e77e33fd61b737e4e3a71
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4206
Tested-by: jenkins
Reviewed-by: Nong Li <nong@cloudera.com>
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4220
Tested-by: Nong Li <nong@cloudera.com>