tools: Generate per-command bash completion script

tools: Generate per-command bash completion script

The current setup uses a single script that is symlinked twice
and that tries to configure bash completion for both virsh and
virt-admin, even if only one of them is installed. This also
forces us to have a -bash-completion RPM package that only
contains the tiny shared file.

Rework bash completion support so that two scripts are
generated, each one tailored to a specific command.

Since the shared script no longer exists after this change,
the corresponding RPM package becomes empty.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>