[µTVM] Clone Zephyr 2.5.0 from maintenance branch (apache#7891)

* [µTVM] Clone Zephyr 2.5.0 from maintenance branch

Clone Zephyr 2.5.0 from maintenance branch 'v2.5-branch' instead of from
release tag 'v2.5.0'. The maintenance branch is stable and includes all
the most recent fixes backported to Zephyr 2.5.0.

Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>

* Retrigger CI

Retrigger CI since the error reported for python3:i386 in test
./tests/scripts/task_python_integration.sh seems to be a CI glitch, not
related to the change here proposed, plus it was not possible to
reproduce it locally, where task_python_integration.sh passes.

docker/install/ubuntu_install_zephyr.sh

@@ -55,7 +55,7 @@ pip3 install west
 #EOF
 #chmod a+x /usr/local/bin/west
 
-west init --mr v2.5.0 /opt/zephyrproject
+west init --mr v2.5-branch /opt/zephyrproject
 cd /opt/zephyrproject
 west update