To check the existance of a namespace, instead of listing the
namespaces directory (by default "/var/run/netns"), this patch
directly checks the existence of the namespace directory, using
"os.path.exists".
This check is faster than listing the whole directory and avoids
timeout problems as reported in the related bug.
Conflicts:
neutron/privileged/agent/linux/utils.py
Closes-Bug: #1947974
Change-Id: I558d50d28378beb3710d98a2113ff9549c82ae17
(cherry picked from commit 8127221479)
(cherry picked from commit 6a9c05a924)