Give .hbase-snapshot proper ownership upon directory creation

This is continuation of the discussion over HBASE-20668.

Tthe .hbase-snapshot directory is not created at cluster startup. Normally it is created when snapshot operation is initiated.

However, if before any snapshot operation is performed, some non-super user from another cluster conducts ExportSnapshot to this cluster, the .hbase-snapshot directory would be created as that user.
(This is just one scenario that can lead to wrong ownership)

This JIRA is to seek proper way(s) to ensure that .hbase-snapshot directory would always carry proper onwership and permission upon creation.