tox: fix test failure on ubuntu 20.04

Fix the following error:

py36 run-test: commands[1] | find /dev/shm -name 'tox_py36*' -delete
/usr/bin/find: ‘/dev/shm/multipath’: Permission denied

We don't care if there are folders in which we cannot enter.
Ignore if the find command fails.

Author: rjarry

tox.ini

@@ -23,9 +23,9 @@ whitelist_externals =
 	/usr/bin/find
 commands =
 	rm -rf '{env:SYSREPO_REPOSITORY_PATH}'
-	find /dev/shm -name '{env:SYSREPO_SHM_PREFIX}*' -delete
+	-find /dev/shm -name '{env:SYSREPO_SHM_PREFIX}*' -delete
 	python -Wd -m unittest discover -c
-	find /dev/shm -name '{env:SYSREPO_SHM_PREFIX}*' -delete
+	-find /dev/shm -name '{env:SYSREPO_SHM_PREFIX}*' -delete
 	rm -rf '{env:SYSREPO_REPOSITORY_PATH}'
 
 [testenv:coverage]
@@ -41,9 +41,9 @@ whitelist_externals =
 	/usr/bin/find
 commands =
 	rm -rf '{env:SYSREPO_REPOSITORY_PATH}'
-	find /dev/shm -name '{env:SYSREPO_SHM_PREFIX}*' -delete
+	-find /dev/shm -name '{env:SYSREPO_SHM_PREFIX}*' -delete
 	python -Wd -m coverage run -m unittest discover -c tests/
-	find /dev/shm -name '{env:SYSREPO_SHM_PREFIX}*' -delete
+	-find /dev/shm -name '{env:SYSREPO_SHM_PREFIX}*' -delete
 	rm -rf '{env:SYSREPO_REPOSITORY_PATH}'
 	python -m coverage report
 	python -m coverage html