Adds a `reboot` option which allows the guest to be rebooted after
the completion of a shell provisioning task. The guest must support
the `:reboot` capability. Like the `reset` option, the `reboot`
option may be provided without defining `inline` or `file` options
when a reboot may be required between other provisioners.
Fixes#8639
of `args` itself and as an element inside of an `args` array. Added validation
around passing in arrays for arguments. Just knowing that it is an array is not
enough, because arrays can contain any other type.
The logic change in 57d4775140 introduced
a bug where neither strings nor arrays provided as `args` for shell
provisioners would pass validation.
This fixes that problem along with a few extras:
- split out arg validation into a private method
- update comment describing valid args
- add a few unit tests around config validation