Set the iso8601 log level to WARN

When use "--debug" parameter in other projects's CLI, it may display
useless iso8601 debug info, this is because  other client's CLI will
call keystoneclient to get token, and keystoneclient will display the
iso8601 debug info.

set the iso8601 log level to "WARN" to avoid this issue.

Change-Id: Id90c86f0e7c8e9ae47ca53667f469d111d6ae373
Closes-bug: #1324470
Merge "Set the iso8601 log level to WARN"