vmw: Fix Printf calls

Spotted by 'go vet':

github.com/cloudius-systems/capstan/hypervisor/vmw/vmw.go:118: no formatting directive in Printf call
github.com/cloudius-systems/capstan/hypervisor/vmw/vmw.go:123: no formatting directive in Printf call
github.com/cloudius-systems/capstan/hypervisor/vmw/vmw.go:136: no formatting directive in Printf call
github.com/cloudius-systems/capstan/hypervisor/vmw/vmw.go:141: no formatting directive in Printf call

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>