Running ginkgo tests in parallel causes problems with dhcp_test.go.
BeforeEach() is run once for each spec before any actual dhcp test starts.
This results in setting up two dhcp4servers that run concurrently.
Both try to Listen and use unix socketPath file /run/cni/dhcp.sock at the same time.
AfterEach() for one test runs when test completes, deleting /run/cni/dhcp.sock.
But other test still needs the file resulting in test failing. Often, the next dhcp
test hasn't started yet. When test does start it waits 15 seconds for dhcp4server to
create /run/cni/dhcp.sock (which has just been deleted) so test fails.
Other times dhcp tests fail because /run/cni/dhcp.sock is deleted while still being used.
