Improve host-add error message

host-add command allows to add a host and its IP address via
--ip-address option. When the address is invalid, it throws
an error and refuses to operate. However, the invalid IP address
error message is always the same which is not right as it forces
a user to guess the reason of rejection (loopback address,
link-local address or invalid address at all was passed, etc.).

This patch changes host-add validator to print the error message.

https://fedorahosted.org/freeipa/ticket/2229

ipalib/plugins/host.py

@@ -203,8 +203,8 @@ def validate_ipaddr(ugettext, ipaddr):
     """
     try:
         ip = CheckedIPAddress(ipaddr, match_local=False)
-    except:
-        return _('invalid IP address')
+    except Exception, e:
+        return unicode(e)
     return None