Using non-existing policy name in policy src or dest leads to error.

If a non-existing policy name is specified in the source or destination of another policy, error is seen in schema transformer.

Steps to reproduce:

1. create a VNs say vn1(10.1.1.0/24)
3. create a policy P12 with rules:
       a. deny protocol icmp network vn1 port any <> NEWPOL port any
       where NEWPOL is name of a policy which is not configured
4. attach the Policy P12 to VN - vn1

<type 'exceptions.NameError'>
Python 2.7.3: /usr/bin/python
Fri Sep 5 15:44:36 2014

A problem occurred in a Python script. Here is the sequence of
function calls leading up to the error, in the order they occurred.

 /usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py in launch_arc(transformer=<schema_transformer.to_bgp.SchemaTransformer object>, ssrc_mapc=<cfgm_common.ifmap.client.client instance>)
 3516 result = arc_mapc.call('poll', pollreq)
 3517 try:
 3518 transformer.process_poll_result(result)
 3519 except Exception as e:
 3520 try:
transformer = <schema_transformer.to_bgp.SchemaTransformer object>
transformer.process_poll_result = <bound method SchemaTransformer.process_poll_res...ema_transformer.to_bgp.SchemaTransformer object>>
result = '<?xml version="1.0" encoding="UTF-8" standalone=...lResult></ns2:response></ns3:Body></ns3:Envelope>'

 /usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py in process_poll_result(self=<schema_transformer.to_bgp.SchemaTransformer object>, poll_result_str='<?xml version="1.0" encoding="UTF-8" standalone=...lResult></ns2:response></ns3:Body></ns3:Envelope>')
 3184 for prule in policy.rules:
 3185 acl_rule_list = virtual_network.policy_to_acl_rule(
 3186 prule, dynamic)
 3187 acl_rule_list.update_acl_entries(acl_entries)
 3188 for arule in acl_rule_list.get_list():
prule = <vnc_api.gen.resource_xsd.PolicyRuleType object>
dynamic = False

 /usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py in policy_to_acl_rule(self=<schema_transformer.to_bgp.VirtualNetworkST object>, prule=<vnc_api.gen.resource_xsd.PolicyRuleType object>, dynamic=False)
 1050 _sandesh._logger.debug(
 1051 "Policy %s not found while applying policy "
 1052 "to network %s", dadr_match.network_policy,
 1053 self.name)
 1054 continue
dadr_match undefined
<type 'exceptions.NameError'>: global name 'dadr_match' is not defined
    __class__ = <type 'exceptions.NameError'>
    __delattr__ = <method-wrapper '__delattr__' of exceptions.NameError object>
    __dict__ = {}
    __doc__ = 'Name not found globally.'
    __format__ = <built-in method __format__ of exceptions.NameError object>
    __getattribute__ = <method-wrapper '__getattribute__' of exceptions.NameError object>
    __getitem__ = <method-wrapper '__getitem__' of exceptions.NameError object>
    __getslice__ = <method-wrapper '__getslice__' of exceptions.NameError object>
    __hash__ = <method-wrapper '__hash__' of exceptions.NameError object>
    __init__ = <method-wrapper '__init__' of exceptions.NameError object>
    __new__ = <built-in method __new__ of type object>
    __reduce__ = <built-in method __reduce__ of exceptions.NameError object>
    __reduce_ex__ = <built-in method __reduce_ex__ of exceptions.NameError object>
    __repr__ = <method-wrapper '__repr__' of exceptions.NameError object>
    __setattr__ = <method-wrapper '__setattr__' of exceptions.NameError object>
    __setstate__ = <built-in method __setstate__ of exceptions.NameError object>
    __sizeof__ = <built-in method __sizeof__ of exceptions.NameError object>
    __str__ = <method-wrapper '__str__' of exceptions.NameError object>
    __subclasshook__ = <built-in method __subclasshook__ of type object>
    __unicode__ = <built-in method __unicode__ of exceptions.NameError object>
    args = ("global name 'dadr_match' is not defined",)
    message = "global name 'dadr_match' is not defined"

The above is a description of an error in a Python program. Here is
the original traceback:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py", line 3518, in launch_arc
    transformer.process_poll_result(result)
  File "/usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py", line 3186, in process_poll_result
    prule, dynamic)
  File "/usr/lib/python2.7/dist-packages/schema_transformer/to_bgp.py", line 1052, in policy_to_acl_rule
    "to network %s", dadr_match.network_policy,
NameError: global name 'dadr_match' is not defined