PAPI: Add support for format/unformat functions.

With the introduction of new types, like vl_api_address_t
it is now possible to call a message using one of those
functions with a string representation. E.g. for an IP address

ip_add_address(address="1.1.1.1/24")

The language wrapper will automatically convert the string
into the vl_api_address_t representation. Currently
the caller must do the reverse conversion from the returned
named tuple with the unformat function.
rv = get_address_on_interface(sw_if_index=1)
print(VPPFormat.unformat(rv.address))

Change-Id: Ic872b4560b2f4836255bd5260289bfa38c75bc5d
Signed-off-by: Ole Troan <ot@cisco.com>
diff --git a/src/vpp-api/python/vpp_papi/vpp_papi.py b/src/vpp-api/python/vpp_papi/vpp_papi.py
index 5e98f92..2310cd1 100644
--- a/src/vpp-api/python/vpp_papi/vpp_papi.py
+++ b/src/vpp-api/python/vpp_papi/vpp_papi.py
@@ -28,6 +28,7 @@
 import atexit
 from . vpp_serializer import VPPType, VPPEnumType, VPPUnionType, BaseTypes
 from . vpp_serializer import VPPMessage, vpp_get_type
+from . vpp_format import VPPFormat
 
 if sys.version[0] == '2':
     import Queue as queue