Replace Integer to Number in Type check

There is no Integer type in Heat template, so we should use Number
instead. See Heat parameters documentation
http://docs.openstack.org/developer/heat/template_guide/hot_spec.html#hot-spec-parameters

IntegerField replaced to FloatField, because Number can store floating
point values too.

Add Type to ValueError message

Change-Id: I74935c7c04cdd980ecc540f14baffbb4d115908c