Fix default case for CNIDir
Fix default case for CNIDir

In case of no-config for CNIDir, multus-cni does not set
defaultCNIDir into CNIDir hence multus-cni failed to create
container network. This change fixes it.

intel/multus-cni,intel/multus-cni,Intel-Corp/multus-cni,Intel-Corp/multus-cni