only install things in the venv for pep8

we can use tox to run tempest, but to act like the gate we
shouldn't install a venv for full or smoke runs.

only do this for pep8, as we need hacking installed from pip

Change-Id: I02a62d3f0ae9759e619976e523f75c64a9af577d
diff --git a/tox.ini b/tox.ini
index b0d66b4..565a9ad 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,8 +9,6 @@
          NOSE_OPENSTACK_YELLOW=3
          NOSE_OPENSTACK_SHOW_ELAPSED=1
          NOSE_OPENSTACK_STDOUT=1
-deps = -r{toxinidir}/tools/pip-requires
-       -r{toxinidir}/tools/test-requires
 
 [testenv:full]
 sitepackages = True
@@ -55,6 +53,8 @@
 
 [testenv:pep8]
 commands = flake8
+deps = -r{toxinidir}/tools/pip-requires
+       -r{toxinidir}/tools/test-requires
 
 [flake8]
 ignore = E125,H302,H404