Allow specifying bcrypt version for htpasswd

[fchan21]

Currently, htpasswd only produces version 2a for hashing which is not accepted in more modern systems. There is a minor security concern with using 2a, so 2y is generally favored. While it might be a bit heavy-handed to force htpasswd to use 2y, it should at least be configurable using additional arguments passed in to the htpasswd function.