Allow the default value of 1 to  be set for boot multiple

Allow one to call the following with their default values of 1:
* nova boot --num-instances 1
* nova boot --min-count 1
* nova boot --max-count 1

Don't allow min_count>max_count.

This is the only place where if a user passes in the default value the
CLI will return an error.

Change-Id: I805b3f0c778e9c70c5817624fb696a746dfe3d5b
Merge "Allow the default value of 1 to  be set for boot multiple"