Shell should use Admin.listTableNames() instead of Admin.listTables()

It seems that getTableDescriptors() in master checks for A and C permissions while getTableNames() checks for any privilege on the table. The reasoning is explained here: https://issues.apache.org/jira/browse/HBASE-12564?focusedCommentId=14234504&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14234504

We should change the shell command for list to use the getTableNames() version because of this. Otherwise a user having only R or W cannot list the table name.

This has been reported from a user here: https://community.hortonworks.com/questions/10742/why-does-a-user-need-create-permission-for-list-co.html#comment-11000.

While we are at it, should we revisit the fact that you cannot get a table descriptor if you have only R or W? It seems strange that you cannot even know the CF names of a table that you can read from. I could not find info about the "describe" privileges on SQL databases. However, if there are use cases where Table descriptor might contain sensitive info, the current semantics seems fine. cc apurtell and mbertozzi.