Use argcomplete for tab completion

[mulkieran]

It is supported wherever we need it.

There are standard tricks to use to install tab completion facilities in an rpm spec file for a Python script.

It should be easy to do this. Our current tab completion facilities are hand-written by an external contributor and are now unmaintained.

Or we could use shtab to just auto-generate tab completion files.

[mulkieran]

Note that argcomplete supports dynamic path completion, for example substituting actual filesystem names when called for, which shtab, which generates these things statically, can not do. On the other hand, argcomplete is much trickier to use and might make users frustrated by slowing things down. What argcomplete would be, potentially, really useful for is long-running testing actions.