Add new build rigging for multi-OS

Given the underlying native library, C lib and other OS lib dependencies
sneak in, so this uses a few different Dockerfiles to build binaries
targetted at specific OSes.

Merge pull request #33 from r2d4/leases

Use last entry when parsing DHCP status file

Add disk cach/io tunables

Often for test scenarios the reliability of the VM isn't important,
but running faster is, so lets expose a few more I/O tunables.

Clean up logging a little

Reduce some of the scary chatter that isn't necessarily bad during
initial startup on a fresh system.

Merge commit '6096a1a39eb1ec6878c797b45afbe0e48410eda0' into rsampaio…

…_conn_fix

Conflicts:
	kvm.go

Sync with machine 0.5.0-rc3

Sync with machine 0.5.0-rc3

Sync with machine 0.5.0-rc3

Sync up to latest plugin model

This brings the kvm driver in sync with the latest version of
docker-archive-public/docker.machine#1902

Minor hardening