hide some sensitive configuration information in the UI

In the discussion about how to store keystore/truststore password securely, bbeaudreault  mentioned and I quote here

"I agree that it seems insecure to put it directly into the hbase-site.xml. Another reason is due to the RS UI which (helpfully) can print the entire site configuration. We’d need to make sure the password is excluded from that, but better to remove it from site xml altogether".

I also felt that some sensitive information was exposed in the UI, for example, if we set superuser in the hbase-site.xml, the non-admin users can obtain superuser information and simulate superuser to perform some non-permitted operations on the cluster. So I think maybe we should hide these sensitive information in the UI.