IMPALA-2331: set null indicators in RowBatchSerializeTest
IMPALA-2331: set null indicators in RowBatchSerializeTest

This correctly initialises all null indicators in RowBatchSerialize test
to not-NULL (i.e. 0 bytes). Previously they were not initialised, so the
tests only passed if the memory happened to be filled with zeroes.

Change-Id: I12edad82ebb8cd7a2fb91b6686555b82f9e133cf
Reviewed-on: http://gerrit.cloudera.org:8080/825
Reviewed-by: Tim Armstrong <2f8e34250f03a653da3dc27f7ec203eafdde80fc@cloudera.com>
Tested-by: Internal Jenkins

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