switch image builds to py3

requirements/requirements.txt

@@ -13,7 +13,6 @@ asn1crypto==0.24.0        # via cryptography
 attrs==17.4.0             # via automat, service-identity
 autobahn==18.3.1          # via daphne
 automat==0.6.0            # via twisted
-backports.functools-lru-cache==1.5  # via jaraco.functools
 baron==0.6.6              # via redbaron
 billiard==3.5.0.4         # via celery
 boto==2.47.0
@@ -24,7 +23,7 @@ constantly==15.1.0        # via twisted
 cryptography==2.3.1       # via requests
 daphne==1.3.0
 defusedxml==0.4.1         # via python-saml
-django-auth-ldap==1.2.8
+django-auth-ldap==1.7.0
 django-crum==0.7.2
 django-extensions==2.0.0
 django-jsonfield==1.0.1
@@ -40,8 +39,6 @@ djangorestframework-yaml==1.0.3
 djangorestframework==3.7.7
 docutils==0.14            # via botocore
 enum34==1.1.6             # via cryptography
-functools32==3.2.3.post2  # via jsonschema
-futures==3.2.0            # via requests-futures
 hyperlink==18.0.0         # via twisted
 idna==2.6                 # via cryptography, hyperlink, requests
 incremental==17.5.0       # via twisted
@@ -78,7 +75,7 @@ pyjwt==1.6.0              # via social-auth-core, twilio
 pyparsing==2.2.0
 pyrad==1.2                # via django-radius
 python-dateutil==2.7.2
-python-ldap==2.5.2        # via django-auth-ldap
+python-ldap==3.1.0        # via django-auth-ldap
 python-logstash==0.4.6
 python-memcached==1.59
 python-openid==2.2.5      # via social-auth-core