In fixing https://github.com/coreos/rpm-ostree/pull/3323
I felt that it was a bit ugly we're installing `/usr/bin/ostree-container`.
It's kind of an implementation detail. We want users to use
`ostree container`.
Let's support values outside of $PATH too.
For example, this also ensures that TAB completion for `ost` expands
to `ostree ` with a space.
Colin Walters