Travis: Turn off Tor's Sandbox in Chutney's CI

We need to set "Sandbox 0", until we fix sandbox errors that are
triggered by Ubuntu Xenial and Bionic. See 32722.

Part of 32630.

.travis.yml

@@ -10,6 +10,21 @@ os:
 
 ## We don't use the build matrix cross-product, because it makes too many jobs
 ## Instead, we list each job under matrix: include:
+env:
+  global:
+    ## Turn off tor's sandbox in chutney, until we fix sandbox errors that are
+    ## triggered by Ubuntu Xenial and Bionic. See #32722.
+    - CHUTNEY_TOR_SANDBOX="0"
+  matrix:
+    ## This matrix entry is required, but it doesn't actually create any jobs
+    ## by itself. All jobs are created by matrix: include: entries
+    ##
+    ## The TOR env var should be kept in sync with the Linux tor version in
+    ## the addons section below
+    ## We use the basic-min network by default, to reduce load and increase
+    ## reliability
+    - TOR="master-nightly" NETWORK_FLAVOUR="basic-min"
+
 matrix:
   # include creates Linux, python 2.7, tor master builds by default
   # we use tor master to catch tor issues before stable releases
@@ -179,12 +194,6 @@ dist: xenial
 ## Recent is Xcode 11.2 on macOS 10.14 as of October 2019
 osx_image: xcode11.2
 
-## The TOR env var should be kept in sync with the Linux tor version below
-## We use the basic-min network by default, to reduce load and increase
-## reliability
-env:
-  - TOR="master-nightly" NETWORK_FLAVOUR="basic-min"
-
 ## Download our dependencies
 addons:
   ## (Linux only)