Update hacking for Python3

The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.

Fix problems found.

Remove hacking and friends from lower-constraints, they are not needed
for installation.

Change-Id: I5f0adcc9fc321848ef93dafc9c2ee2d4061a1cbc

ldappool/__init__.py

@@ -250,7 +250,7 @@ class ConnectionManager(object):
         # each one in turn in case of connection failures (server down,
         # timeout, etc.).  URIs can be delimited by either commas or
         # whitespace.
-        for server in re.split('[\s,]+', self.uri):
+        for server in re.split(r'[\s,]+', self.uri):
             tries = 0
             exc = None
             conn = None

lower-constraints.txt

@@ -5,9 +5,6 @@ docutils==0.11
 dulwich==0.15.0
 extras==1.0.0
 fixtures==3.0.0
-flake8-docstrings==0.2.1.post1
-flake8==2.5.5
-hacking==0.12.0
 imagesize==0.7.1
 Jinja2==2.10
 linecache2==1.0.0
@@ -16,9 +13,7 @@ mccabe==0.2.1
 openstackdocstheme==1.18.1
 pbr==2.0.0
 pep257==0.7.0
-pep8==1.5.7
 prettytable==0.7.2
-pyflakes==0.8.1
 Pygments==2.2.0
 python-ldap==3.0.0
 python-mimeparse==1.6.0

test-requirements.txt

@@ -3,7 +3,7 @@
 # process, which may cause wedges in the gate later.
 # of appearance.
 
-hacking>=1.1.0,<1.2.0 # Apache-2.0
+hacking>=3.0,<3.1.0 # Apache-2.0
 flake8-docstrings==0.2.1.post1 # MIT
 
 coverage!=4.4,>=4.0 # Apache-2.0