Attempt to fix tox installs

changelog.d/4124.misc

@@ -0,0 +1 @@
+Fix `tox` failure on old systems

jenkins/prepare_synapse.sh

@@ -14,22 +14,3 @@ fi
 
 # set up the virtualenv
 tox -e py27 --notest -v
-
-TOX_BIN=$TOX_DIR/py27/bin
-
-# cryptography 2.2 requires setuptools >= 18.5.
-#
-# older versions of virtualenv (?) give us a virtualenv with the same version
-# of setuptools as is installed on the system python (and tox runs virtualenv
-# under python3, so we get the version of setuptools that is installed on that).
-#
-# anyway, make sure that we have a recent enough setuptools.
-$TOX_BIN/pip install 'setuptools>=18.5'
-
-# we also need a semi-recent version of pip, because old ones fail to install
-# the "enum34" dependency of cryptography.
-$TOX_BIN/pip install 'pip>=10'
-
-{ python synapse/python_dependencies.py
-  echo lxml
-} | xargs $TOX_BIN/pip install

tox.ini

@@ -11,6 +11,20 @@ deps =
     # needed by some of the tests
     lxml
 
+    # cyptography 2.2 requires setuptools >= 18.5
+    #
+    # older versions of virtualenv (?) give us a virtualenv with the same
+    # version of setuptools as is installed on the system python (and tox runs
+    # virtualenv under python3, so we get the version of setuptools that is
+    # installed on that).
+    #
+    # anyway, make sure that we have a recent enough setuptools.
+    setuptools>=18.5
+
+    # we also need a semi-recent version of pip, because old ones fail to
+    # install the "enum34" dependency of cryptography.
+    pip>=10
+
 setenv =
     PYTHONDONTWRITEBYTECODE = no_byte_code