[neutron] Rely on PATH env set by devstack

This was missed as part of [1], neutron sets
exec_dirs in rootwrap.conf differently so that
also needs to be fixed.

Without it neutron openvswitch jobs relying on
neutron-keepalived-state-change scripts were
failing when deployed with GLOBAL_VENV=True as
binaries no longer found at /usr/local/bin.

[1] https://review.opendev.org/c/openstack/devstack/+/558930

Closes-Bug: #2031415
Change-Id: I9aa56bff02594f253381ffe47a70949079f4c240
1 file changed