Add a virtualenv-based python bootstrapping service to infra.

DEPS

 deps = {
   "build":
     "https://chromium.googlesource.com/chromium/tools/build.git",
 
   "depot_tools":
     "https://chromium.googlesource.com/chromium/tools/depot_tools.git",
 
   ## external deps
-  # v0.8.0
-  "infra/infra/ext/argcomplete":
-    ("https://chromium.googlesource.com/infra/third_party/argcomplete.git"
-     "@a88dcaae3132003ae123d39a2cd9924113b8f985"),
-
-  # v1.5 (v2 requires more dependencies)
-  "infra/infra/ext/dateutil":
-    ("https://chromium.googlesource.com/infra/third_party/python_dateutil.git"
-     "@731ee1ce8456361eba2c619e90989f6db45625b9"),
-
-  # master at 2014-05-03 9:27-4
-  "infra/infra/ext/httplib2":
-    ("https://chromium.googlesource.com/infra/third_party/httplib2.git"
-     "@7d1b88a3cf34774242bf4c0578c09c0092bb05d8"),
-
-  # master at 2014-06-25 15:56-7
-  "infra/infra/ext/oauth2client":
-    ("https://chromium.googlesource.com/infra/third_party/oauth2client.git"
-     "@1a3a99f11369806d7c517350df0b95ec50c317dd"),
-
-  # master at 2014-06-02 12:44+0
-  "infra/infra/ext/pytz":
-    ("https://chromium.googlesource.com/infra/third_party/pytz.git"
-     "@056207cdda4a8f01f7f0bd924e89d0df434c7547"),
-
-  # v2.3.0
-  "infra/infra/ext/requests":
-    ("https://chromium.googlesource.com/infra/third_party/requests.git"
-     "@6366d3dd190a9e58ca582955cddf7e2ac5f32dcc"),
+  # v1.11.6
+  "infra/bootstrap/virtualenv":
+    ("https://github.com/pypa/virtualenv.git"
+     "@93cfa83481a1cb934eb14c946d33aef94c21bcb0"),
 }
 
 hooks = [
   {
     "pattern": ".",
     "action": [
-      "python", "-u", "infra/run.py",
-      "infra.tools.bootstrap.get_appengine", "--dest=..",
+      "python", "-u", "./infra/bootstrap/bootstrap.py", "--deps_file",
+      "infra/bootstrap/deps.pyl", "infra/ENV"
+    ],
+  },
+  {
+    "pattern": ".",
+    "action": [
+      "python", "-u", "./infra/bootstrap/get_appengine.py", "--dest=.",
     ],
   },
 ]
 
 recursion = 1