RFR (XS) 6417649: -interval=0 is accepted and jconsole doesn't update window content at all

[Erik Gahlin]

Please review a small change.

Description:
-interval=0 command line option is accepted. In this case jconsole 
doesn't update content at all. It seems that such functionality is 
useless for an ordinary user.

Solution:
If interval of zero or less is specified the help text shown, similar to 
how to other invalid input is handled today.

Bug:
http://monaco.us.oracle.com/detail.jsf?cr=6417649

Webrev:
http://cr.openjdk.java.net/~egahlin/6417649/

Testing:
Verified that negative and zero is not accepted on command line

A sponsor is needed.

Thanks
Erik