Don't allow service-add to create host/ principals

ipalib/errors.py

@@ -356,6 +356,10 @@ class DefaultGroup(ConfigurationError):
     """You cannot remove the default users group"""
     faultCode = 1025
 
+class HostService(ConfigurationError):
+    """You must enroll a host in order to create a host service"""
+    faultCode = 1026
+
 class FunctionDeprecated(GenericError):
     """Raised by a deprecated function"""
     faultCode = 2000

ipalib/plugins/f_service.py

@@ -72,6 +72,9 @@ class service_add(crud.Add):
             raise errors.MalformedServicePrincipal
         service = sp[0]
 
+        if service.lower() == "host":
+            raise errors.HostService
+
         sr = sp[1].split('@')
         if len(sr) == 1:
             hostname = sr[0].lower()