Checks if the specified bank contains the specified key.

def contains(bank, key):
    '''
    Checks if the specified bank contains the specified key.
    '''
    if key is None:
        return True  # any key could be a branch and a leaf at the same time in Consul
    else:
        try:
            c_key = '{0}/{1}'.format(bank, key)
            _, value = api.kv.get(c_key)
        except Exception as exc:
            raise SaltCacheError(
                'There was an error getting the key, {0}: {1}'.format(
                    c_key, exc
                )
            )
        return value is not None