CNI CMD Add - Avoid relying on err var in cleanup

[adrianchiris]

Currently if cmdAdd function fails, we rely on top level err error variable to determine if cleanup needs to occur via defer statements [1]
This is brittle as err variable may be re-declared in inner-scope masking it and in case of error in inner scope causing the deferred functions to behave in an un-desirable manner (essentially do nothing)

we should come up with a better mechanism for cleanup. it might not look pretty but it should be more robust.

[1]

sriov-cni/cmd/sriov/main.go

Line 113 in 2aea1bb

defer func() {