Make ssh and ps consider all vmstores by default

Currently, `transient ps` and `transient ssh` will only list or connect to VMs created within the provided (via flag, environment variable, or default) vmstore location. The intent behind this was to make separate vmstores behave totally separately, and allow them to have overlapping names and such. However, I know think that this behavior should be opt-in. So there would be a `--local` flag or something that would cause the current behavior, but by default VMs in all VMStores would be searched (just for the running VMs and SSH, the offline VMs listed by `transient ps -a` would still only show things in the current store as there is no practical way of finding other vmstores with no running VMs).

The motivation here is that sometimes test infrastructure and such starts VMs with an isolated vmstore, and it can be annoying and confusing to not be able to find the VMs you know are running. If this approach isn't taken then there should at least be a `--global` flag or something that does not limit things to the current vmstore.