Replace veewee with packer

Signed-off-by: David Scott <dave.scott@citrix.com>
Remove puppet, add xen

Signed-off-by: David Scott <dave.scott@citrix.com>
updated URL to ISO for Debian 7.5.0;
added @mor1's Vagrantfile and provisioning scripts, from https://github.com/mirage/mirage-vagrant-vms/tree/d00d7cf298b9908f30830ba884010f0b13aff8f3
updated Debian version, to be the same used in the Packer definition;
renamed into the file expected in template.json;
updated opam version to 1.2 from 1.1.1;
fixed quoting -- was getting unexpected end of line error;
added step;
setup was failing because it couldn't find scp, so added line to install it;
fixed specification of opam version;
added 'make lib-ext' step since opam building was failing because of missing dependencies -- the error message suggested adding this step;
tweaked names of shared directories;
added -f, since was getting non-zero status since no files were found to delete, and this was being interpreted as an error;
updated readme;
minor;
merged https://github.com/niksu/mirage-vagrant-vms/tree/provisioning