Use a common base req file to avoid tox double requirements.

requirements/edx/base.txt

@@ -52,7 +52,6 @@ edx-django-oauth2-provider==1.2.5
 edx-django-sites-extensions==2.3.0
 edx-enterprise==0.55.4
 edx-oauth2-provider==1.2.2
-edx-opaque-keys==0.4.0
 edx-organizations==0.4.9
 edx-rest-api-client==1.7.1
 edx-search==1.1.0
@@ -95,7 +94,6 @@ social-auth-core==1.4.0
 pytz==2016.7
 pysrt==0.4.7
 PyYAML==3.12
-requests==2.9.1
 requests-oauthlib==0.4.1
 rules==1.1.1
 scipy==0.14.0
@@ -113,7 +111,6 @@ unicodecsv==0.14.1
 django-require==1.0.11
 django-webpack-loader==0.4.1
 pyuca==1.1
-wrapt==1.10.5
 zendesk==1.1.1
 
 # lxml is also in requirements/edx-sandbox/post.txt
@@ -160,7 +157,6 @@ django_nose==1.4.1
 factory_boy==2.8.1
 flaky==3.3.0
 freezegun==0.3.8
-mock==1.0.1
 moto==0.3.1
 needle==0.5.0
 nose==1.3.7
@@ -210,3 +206,5 @@ XBlock==1.1.1
 
 # Redis version
 redis==2.10.6
+
+-r base_common.txt

requirements/edx/base_common.txt

+# These requirements are needed by both paver.txt and base.txt currently.
+# When tox builds an environment with multiple requirements files and finds
+# the same package listed multiple times, it'll fail to build the tox environment.
+# Using a common base requirements file and '-r' including it in other files
+# works around the tox issue.
+#
+# We plan to move edx-platform to use pip-tools soon and each target will have its
+# own requirements files built, which will remove the need for this file.
+wrapt==1.10.5
+edx-opaque-keys==0.4.0
+requests==2.9.1
+mock==1.0.1

requirements/edx/paver.txt

 # Requirements to run and test Paver
 Paver==1.2.4
 libsass==0.10.0
-wrapt==1.10.5
 markupsafe
-edx-opaque-keys
-requests
-mock
\ No newline at end of file
+-r base_common.txt