fix(install.sh): accept a version argument and anticipate non-root installs

This allows users to invoke our install.sh script using a version other than the latest: `install.sh v0.12.0`.

Also adds some logic to CoreOS installs to ensure that we explicitly refresh units into /var/lib/deis/units, anticipating the impending change to `deisctl`'s behavior.

This should be totally backward compatible. Tested as much as I can.