Make sure msgpack-python version >= 0.4.0

Now Marconi is using on msgpack and relaying on a new feature
introdcued in msgpack since 0.4.0. If user are using the version
under that, they may run into HTTP 503 code for some operations.

Change-Id: Ib24318c3d593f3d2d0625d0f2c582e26d81f43d1
Closes-Bug: 1331280
Merge "Make sure msgpack-python version >= 0.4.0"