A fix to address golint warning

[shuklanirdesh82]

Fixes #1601

make build-all output:

with out the fix:

../misc/scripts/build.sh build
make: Entering directory `/go/src/github.com/vmware/docker-volume-vsphere/client_plugin'
../tests/utils/dockercli/containers.go:127:53: should replace i += 1 with i++
go tool vet .
gofmt -s -l -w .

with fix:

../misc/scripts/build.sh build
make: Entering directory `/go/src/github.com/vmware/docker-volume-vsphere/client_plugin'
go tool vet .
gofmt -s -l -w .