Add "enable_pwd_validator" variable to apply password
validator settings when enabled in horizon values.
Modify "PASSWORD_VALIDATOR" so as to enforce password
requirements i.e., password must be at least eight
characters in length and must include characters from
at least two of these groupings: alpha, numeric, and
special characters when "enable_pwd_validator" is enabled.
Change-Id: Ia866feb875490d0bb40e820c6c32ee2cb6aa4c29