Of note: The rpm/yum thing seems to be coupled, so I put it into one
function that tries the yum helper and uses the rpm path otherwise.
Zypper is already its own thing, so this should only be used for yum
and probably dnf (does that still have the helper?)
Zypper can be dropped, as that already used a separate function in the file.
Apk can just be inlined - it's literally one line for installed and another for all packages.
The `snap interfaces` command prints out a deprecation notice to stderr. This breaks the completion
support for interfaces, connect and disconnect commands like so:
```
$ snap connect <TAB>error: no interfaces found
error: no interfaces found
...
'snap interfaces' is deprecated; use 'snap connections'.
'snap interfaces' is deprecated; use 'snap connections'.
'snap interfaces' is deprecated; use 'snap connections'.
error: no interfaces found
error: no interfaces found
'snap interfaces' is deprecated; use 'snap connections'.
```
Ultimately, the snap command completion should switch to `snap connections`. However, for now try to
workaround the notice by redirecting stderr.
Signed-off-by: Maciek Borzecki <maciek.borzecki@gmail.com>
