This adds three new subcommands: importer-service-poller,
importer-service-broker and importer-service-worker.
I had a choice here: I could have added new snap endpoints as was done
previously with import-source-packages.py becoming
git-ubuntu.import-source-packages, but I think I prefer moving all
endpoints into git-ubuntu subcommands now that we have these, so I did
this instead.
The user expectation is that the user's host ssh configuration be used.
We are therefore dependent on the host system having ssh and it
functioning correctly. So just use it.
This fixes version mismatches between the ssh shipped in the snap and
the host ssh configuration file format, as well as library dependency
mismatches.
We haven't been setting up LD_LIBRARY_PATH for bash from the core snap,
so host system libraries were being linked. This then breaks on a Focal
host because the libraries needed by bash in the core snap are no longer
available on the host.
We could work around this by setting LD_LIBRARY_PATH, but it is in
general dangerous to call binaries from the core snap from a classic
snap because we don't have control over how they might interact with the
host system.
Instead, we ship bash in our own snap via "stage-packages" and adjust
the shebangs to use this instead.
