[docker] Clarify how to run Impala in standalone
[docker] Clarify how to run Impala in standalone

Change-Id: Ib5feec357f554b72856a39d0209c60b91d9816e0
Reviewed-on: http://gerrit.cloudera.org:8080/15810
Tested-by: Kudu Jenkins
Reviewed-by: Attila Bukor <53758272babe3057a5ff4ad51afd9bfd6e6014a1@apache.org>
Reviewed-by: Grant Henke <4cf7ebbe638391c4d27a10cf751b99bdbd1a1880@apache.org>

helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu