add machine readable logging, action starts/ends

This PR adds start/stop machine logging on all machine actions.
Also added are :info, :warn, etc. logging in machine readable format.

ex:

% vagrant --machine-readable provision
1403294532,repo.vagrant-tj,action,provision:start:LXC (repo_repovagrant-tj_1403125397237_26227)
1403294532,repo.vagrant-tj,info,Running provisioner: shell...
1403294532,repo.vagrant-tj,action,fetch_ip:start:LXC (repo_repovagrant-tj_1403125397237_26227)
1403294532,repo.vagrant-tj,action,fetch_ip:end:LXC (repo_repovagrant-tj_1403125397237_26227)
1403294532,repo.vagrant-tj,action,fetch_ip:start:LXC (repo_repovagrant-tj_1403125397237_26227)
1403294532,repo.vagrant-tj,action,fetch_ip:end:LXC (repo_repovagrant-tj_1403125397237_26227)1403294533,repo.vagrant-tj,detail,Running: /tmp/vagrant-shell20140620-3686-13gcohz.sh
1403294533,repo.vagrant-tj,info,Loaded plugins: fastestmirror%!(VAGRANT_COMMA) priorities
1403294533,repo.vagrant-tj,info,Loading mirror speeds from cached hostfile
1403294554,repo.vagrant-tj,info,Running provisioner: shell...
1403294554,repo.vagrant-tj,action,fetch_ip:start:LXC (repo_repovagrant-tj_1403125397237_26227)
1403294554,repo.vagrant-tj,action,fetch_ip:end:LXC (repo_repovagrant-tj_1403125397237_26227)
...
1403294555,repo.vagrant-tj,detail,Running: inline script1403294555,repo.vagrant-tj,action,provision:end:LXC (repo_repovagrant-tj_1403125397237_26227)
1403294555,repo.vagrant-tj,action,provision:end:LXC (repo_repovagrant-tj_1403125397237_26227)