uvtool updates

[Robie Basak]

Now available from the new ppa:uvtool-dev/master:

* --insecure is no longer required
* Snapshots now work (thanks to Chris Arges)
* New --no-start option (thanks to Tycho Andersen)
* "wait" no longer hangs in a race with a newer dnsmasq

I've moved uvtool development to git on Launchpad, with a new source
build recipe to keep the PPA up-to-date automatically. You should be
able to get the latest uvtool from ppa:uvtool-dev/master for Trusty,
Xenial, Yakkety and possibly Precise. The old ppa:uvtool-dev/trunk that
followed bzr development is now deprecated. If you had the old PPA
enabled, you should be able to replace "trunk" with "master" in
sources.list or sources.list.d/uvtool... etc.

Since we're beyond Yakkety's feature freeze, I intend to upload this to
Ubuntu for the release after Yakkety. I can cherry-pick bugfixes to
Yakkety in the meantime though.

Bugs and things still exist - it's mainly the tech debt and some
outstanding merge proposals that I've caught up on here.

Known issues:

 * Though snapshots work, "uvt-kvm destroy <name>" on a VM with a
   snapshot makes uvtool fall over. The workaround is to use virsh to
   remove the snapshot first, or to use virsh to both remove the
   snapshot and undefine the VM after a uvt-kvm destroy failure. LP:
   #1623947.