Add Provisioner Banners and Timings

[tomjn]

It isn't clear when one site is done and the next one starts. We should make this clear and add a start/finish message with the time elapsed.

VVV does this for the main provisioners, but given the meta environment can take a while, it would be good to do this internally:

The other benefit of this is that we can direct most of the output to the log file so only errors and progress indicators are shown in the terminal