ignore-patterns does not skip non-top-level directories.

[natedogith1]

Steps to reproduce

1. create a a/b/c.py (where c.py will generate a pylint message, so that we get output) (along with the appropriate __init__.py files)
2. Run pylint: pylint --ignore-patterns=b
3. Run pylint: pylint --ignore-patterns=a

Current behavior

c.py is skipped for ignore-patterns=a, but not for ignore-patterns=b

Expected behavior

c.py should be skipped for both

pylint --version output

pylint 2.1.1
astroid 2.1.0-dev
Python 3.6.3 (v3.6.3:2c5fed8, Oct 3 2017, 17:26:49) [MSC v.1900 32 bit (Intel)]