Fix Ansible version requirement for CentOS6 and 7

CentOS 6 and 7 ship with setuptools 0.9.8, which is too old to cope
with the ~= notation; PEP 440 version specifiers were fully implemented
only starting setuptools 8.0.

So let's use a compatible specifier, implemented in terms of
basic version comparison operators.

setup.py

@@ -58,7 +58,7 @@ def ansible_pb_files():
 required_packages = [
     'PyCLI',
     'paramiko',
-    'ansible~=1.9.4',
+    'ansible>=1.9.4, <2.0.0',
     'voluptuous>=0.8.2',
     'configobj',
     'coloredlogs',