Remove 'readline' from the setup.py
Remove 'readline' from the setup.py

`networking-midonet` (formely `python-neutron-plugin-midonet` project)
has been added into CI infrastructure workflow. When PMC is installed,
it installs all of its dependences.  Unfortunately, `readline` is a
compiled dependency and CI machines does not have the headers to build
them. So it fails building it.

Since `readline` is just needed for command line, maybe the best we can
do without too much changes is avoid its installation for python
packages.

Change-Id: I96e06a16688fea2cd9bf5d5edc7153f65db917b2

celebdor/python-midonetclient,celebdor/python-midonetclient