added the ability to edit the vm mac address
added the ability to edit the vm mac address
edited REDME with mac address instructions
Merge branch 'master' into dataplayer-master

Conflicts:
	README.md
Update README and specs for MAC address setting.
MAC: modify VM spec, don't use ReconfigVM_Task

Using the `ReconfigVM_Task` does not work when cloning a VM from a
template, rather than another VM, so we modify `spec`, similar to how
`add_custom_cpu` and `add_custom_memory` modify `spec`.

`add_custom_mac` and `add_custom_vlan` both change an array of
`VirtualDeviceConfigSpec` objects, but if the user has both options
specified, then the changes apply to the same object. To handle this,
`modify_network_card` uses an instance variable `@card` for *the*
network card, and ensures that the array `spec[:config][:deviceChange]`
never has duplicate values.

Additionally, change how `card.backing` is set in `add_custom_vlan`; see
https://github.com/keymon/knife-vsphere/commit/548fb8cd5204382e92d35f55a0fcd645b09fe429

This change addresses my comments on [GH-108].
Merge branch 'dataplayer-master'