Fix for EUCA-5921 - Windows computer name change

This is a fix for handling the use case when a user wants to change the
computer name of an instance that has been launched on Eucalyptus.  It
checks to see if the instance is newly launched.  If it is, then it will
set the hostname to the instance id.  If the instance has been launched
before, then it will allow user-initiated computer name changes, which
calls for a reboot of the instance.  This works for instance that are
bound to Active Directory as well since Active Directory relies on the
SID of the computer object, not the computer name.  Thanks to Deependra
Shekhawat for helping out with the  solution and testing of this patch.