Fix data race in simulator.container.id
Fix data race in simulator.container.id

This patch fixes a bug where a data race would occur around
access to the simulator.container.id field. The race could
be produced by running the following test:

    go test -run Example_runContainer -v -race -count 1 ./simulator

With this patch, the race no longer occurs, and the container
is also now thread safe.

bruceadowns/govmomi,vmware/govmomi,vmware/govmomi,bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi