Switch to msgpack in pip-requires
msgpack-python got renamed to msgpack[1] so use the new name.
[1]
Acked-By: Iwase Yusuke
# following issue.
# https://github.com/eventlet/eventlet/issues/401
eventlet!=0.18.3,>=0.18.2,!=0.20.1,<0.21.0
-msgpack-python>=0.3.0 # RPC library, BGP speaker(net_cntl)
+msgpack>=0.3.0 # RPC library, BGP speaker(net_cntl)
netaddr
oslo.config>=1.15.0
ovs>=2.6.0 # OVSDB
