Merge "ensure_dir: move under neutron.common.utils"

diff --cc neutron/agent/linux/dhcp.py
Simple merge

diff --cc neutron/agent/linux/utils.py
Simple merge

diff --cc neutron/tests/unit/agent/l3/test_agent.py
Simple merge

diff --cc neutron/tests/unit/agent/linux/test_dhcp.py
Simple merge