IMPALA-5772: also fix TestScratchLimit
IMPALA-5772: also fix TestScratchLimit

This reduces the scratch limit to the same value as used in
TestScratchDisk.

Change-Id: If5c42b6ded44d86c3a430a983096f14c0b88a287
Reviewed-on: http://gerrit.cloudera.org:8080/7664
Reviewed-by: Sailesh Mukil <a0dfbcae8e92bb4f48772d8c6743e175570f6f74@cloudera.com>
Tested-by: Impala Public Jenkins

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala