IMPALA-3470: DecompressorTest is flaky.
IMPALA-3470: DecompressorTest is flaky.

Make sure the random number is greater than 0 and stream is indeed truncated.

Change-Id: I7ebaa403abf45e31f38d6cf4e557d6274d877a8a
Reviewed-on: http://gerrit.cloudera.org:8080/3954
Reviewed-by: Juan Yu <34a62e20de6070542c7bca4f0f49d6e4786ad51e@cloudera.com>
Tested-by: Internal Jenkins

michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala