gnt-instance info: automatically request locking

Commit dae661a4 added support for controlling the locking, but it
didn't modify the gnt-instance info code, which leads to this command
always showing:

Wed Apr 20 04:10:48 2011  - WARNING: Non-static data requested, locks
need to be acquired

We simply change gnt-instance to request locks whenever we don't use
the static mode.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>