[Trivial] set min max_over_subscription_ratio to 1
This change sets the 'max_over_subscription_ratio' config option
minimum value to '1'.
The minimum value is already documented in the config option help
field but is not enforced.
This change allows simplifying code that performs config validation.
@@ -159,6 +159,7 @@ volume_opts = [
'storage if the driver supports it.'),
cfg.FloatOpt('max_over_subscription_ratio',
default=20.0,
+ min=1,
help='Float representation of the over subscription ratio '
'when thin provisioning is involved. Default ratio is '
'20.0, meaning provisioned capacity can be 20 times of '
