Use short option for lvchange

- The `lvchange` command has inconsistent long options for activating
a volume. The CentOS 6.5 and Ubuntu 14.04 have `--activate` where as
the old Ubuntu and CentOS platforms have `--available` command line
flags. To make things consistent, let's use the short option `-a`
as it is consistent across platforms and their versions.
- Also use `lv.state` instead of `lv.active` as that seems to give
consistent results as well.