`saveEnv` had a flag which would prevent an environment from being
overwritten if it already existed, which was only used by `lumi env
init`. Refactor the code so the check is done inside `lumi` instead of
against this API. We don't need this functionality for the service and
so requiring support for this at the API boundary for environments
feels like a bad idea.
We'd like to abstract out environment CRUD operations and I'd prefer
not to have to bake in the conspect of a file name like thing in the
abstraction. Since we were not really using this feature many places,
let's just get rid of it.
The implementation of these functions will be moving out of the engine
and into `lumi` itself, it's a little easier if we move away from
spewing stuff to the diag interface, so just use glog instead (which
`lumi` already uses for logging)
This refactors the engine so all of the APIs on it are instance
methods on the type instead of raw methods that float around and use
data from a global engine.
A mechcanical change as we remove the global `E` and then make
anything that interacted with that in pkg/engine to be an instance
method and the dealing with the fallout.
Instead of talking directly to stdout or stderr via methods on fmt,
indirect through an Engine type (presently a global, but soon to
change) to allow control of where the streams actually end up.
Prevously, we would throw raw args arrays across the interface and the
engine would do some additional parsing. Clean this up so we don't do
that and all the parsing stays in `lumi`
