Fix build

- Adjust format to make it tox-4 compatible
- Rename blacklist_externals to allowlist_externals
- Add {toxinidir}/tools/lxd_build.sh to allowlist

Change-Id: I2dc03dfb39e1cee3248c7cbf46290d7b48901742

tox.ini

@@ -7,10 +7,13 @@ basepython = python3
 install_command = pip install {opts} {packages}
 setenv =
     PATH = /snap/bin:{env:PATH}
-passenv = HOME TERM
-whitelist_externals =
+passenv =
+    HOME
+    TERM
+allowlist_externals =
     sudo
     /snap/bin/snapcraft
+    {toxinidir}/tools/lxd_build.sh
 
 [testenv:snap]
 deps = -r{toxinidir}/requirements.txt