IMPALA-5072: Fix test_recover_partitions on S3
IMPALA-5072: Fix test_recover_partitions on S3

On S3, directory creation is a nop, so we have to actually
create values to materialize the partitions.

Was able to merge this against my fork and successfully ran
the metadata/test_recover_partitions test on S3.  Also ran
locally to verify there is no slowdown for HDFS.

Change-Id: I30d86e49b000db925a778ff53479b61a075dc88c
Reviewed-on: http://gerrit.cloudera.org:8080/6408
Reviewed-by: Michael Brown <97e4d5d0e400e5ad37382425ea95bde8b3933403@cloudera.com>
Reviewed-by: Dimitris Tsirogiannis <285e4b680d94e4ded69b0d5c81922fd12d83ee6c@cloudera.com>
Tested-by: Impala Public Jenkins

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