Travis: Only run IPv6 chutney tests on macOS

Run the test-network-ipv6 Makefile target in the Travis CI IPv6 chutney
job. This job runs on macOS, so it's a bit slow.

Closes ticket 33303.

.travis.yml

@@ -34,6 +34,8 @@ env:
     ## 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"
+    ## The default target for chutney jobs
+    - CHUTNEY_MAKE_TARGET="test-network-all"
   matrix:
     ## This matrix entry is required, but it doesn't actually create any jobs
     -
@@ -77,7 +79,8 @@ matrix:
     #  compiler: clang
     #  os: osx
     ## We run chutney on macOS, because macOS Travis has IPv6
-    - env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes"
+    ## But we only run the IPv6 chutney tests, to speed up the job
+    - env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes" CHUTNEY_MAKE_TARGET="test-network-ipv6"
       os: osx
     ## We clone our stem repo and run `make test-stem`
     - env: TEST_STEM="yes" SKIP_MAKE_CHECK="yes"
@@ -97,7 +100,7 @@ matrix:
     - env: RUST_VERSION="nightly" RUST_OPTIONS="--enable-rust --enable-cargo-online-mode"
       compiler: clang
       os: osx
-    - env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes"
+    - env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes" CHUTNEY_MAKE_TARGET="test-network-ipv6"
       os: osx
 
 ## (Linux only) Use a recent Linux image (Ubuntu Bionic)
@@ -230,7 +233,7 @@ script:
   ## We run `make check` because that's what https://jenkins.torproject.org does.
   - if [[ "$SKIP_MAKE_CHECK" == "" ]]; then make check; fi
   - if [[ "$DISTCHECK" != "" ]]; then make distcheck DISTCHECK_CONFIGURE_FLAGS="$CONFIGURE_FLAGS"; fi
-  - if [[ "$CHUTNEY" != "" ]]; then make test-network-all; fi
+  - if [[ "$CHUTNEY" != "" ]]; then make "$CHUTNEY_MAKE_TARGET"; fi
   ## Diagnostic for bug 29437: kill stem if it hangs for 9.5 minutes
   ## Travis will kill the job after 10 minutes with no output
   - if [[ "$TEST_STEM" != "" ]]; then make src/app/tor; timelimit -p -t 540 -s USR1 -T 30 -S ABRT python3 "$STEM_SOURCE_DIR"/run_tests.py --tor src/app/tor --integ --test control.controller --test control.base_controller --test process --log TRACE --log-file stem.log; fi

changes/ticket33303

@@ -0,0 +1,4 @@
+  o Testing:
+    - Run the test-network-ipv6 Makefile target in the Travis CI IPv6 chutney
+      job. This job runs on macOS, so it's a bit slow.
+      Closes ticket 33303.