This returns the number of hourly instances an account can add from this point.
This returns the number of hourly instances an account can add from this point. It is essentially the same as SoftLayer_Account::hourlyInstanceLimit minus existing hourly instances and ones spoken for as part of a scaling group (as determined by the group's maximum). This number can be used to help determine a maximum member count for a new group to ensure it won't go over the account limit. This can return a negative value if the current hourly instance count combined with the unused-but-possible count (based on other scale group maximums) is over the limit.