Add options to host.autostart.add

[weinrea]

This is to allow for per VM config to the HostAutoStartManager.
Also useful to configure an ordered auto startup.

Example:
govc host.autostart.add -start-order=1 -start-delay=5 vm1 vm2
govc host.autostart.add -start-order=3 -start-delay=30 vm3

Tested on ESXi 6.0.0

[vmwclabot]

@weinrea, you must sign our contributor license agreement before your changes are merged. Click here to sign the agreement. If you are a VMware employee, read this for further instruction.

[vmwclabot]

@weinrea, VMware has approved your signed contributor license agreement.

[dougm]

@weinrea nice, thanks