Put more of the Tox setup in the setup step

This will give more accurate test step timings.

.circleci/config.yml

@@ -90,9 +90,14 @@ jobs:
             # suite as a non-root user.  See below.
             sudo --set-home -u nobody virtualenv --python python2.7 /tmp/tests
             sudo --set-home -u nobody /tmp/tests/bin/pip install tox codecov
+            # Get everything installed in it, too.
+            sudo --set-home -u nobody /tmp/tests/bin/tox -c /tmp/project/tox.ini --workdir /tmp --notest -e ${TAHOE_LAFS_TOX_ENVIRONMENT}
 
       - run: &RUN_TESTS
           name: "Run test suite"
+          # Something about when it re-uses an existing environment blows up
+          # if the working directory is not readable.
+          working_directory: "/tmp"
           command: |
             # Run the test suite as a non-root user.  This is the expected
             # usage some small areas of the test suite assume non-root