Cudet doesn't filter nodes by role

Detailed bug description:
Cudet tool fails to filter nodes by the given role when applying custom filter (via custom configuration file).

Steps to reproduce:
1 Deploy a 9.1 cluste, e.g. 1 controller + 1 compute + 1 cinder nodes
2 Install Cudet
  yum install -y python-cudet
3 CD to /usr/share/cudet/
4 Update cudet-config.yaml Cudet config file - set a role to filter by in [filters][roles] list type parameter
5 Run the tool specifying config file to use
  cudet -c ./cudet-config.yaml

Expected result: the tool is executed according to filter parameters specified in the config file.
Actual result: command execution returns 'No valid nodes were found which could fit filter parameters.' message.

It looks like the problem is in this method (cudet/nodes.py module):
    def _do_filter(self, nodes_info, attr):
        return [node for node in nodes_info
                if node.get(attr) in self.filters[attr]]

In case of filtering by role the node.get(attr) expression returns a list, e.g. ['cinder'], and filter values are also provided in lists.
So in case of filtering by role there is "['cinder'] in ['cinder']" check for the mentioned case.

Description of the environment:
MOS 9.1, snapshot #251.