Implement fake completion support for multi-cmd binaries
Implement fake completion support for multi-cmd binaries

This will allow build-bash-completion to understand what is the list
of commands that each binary supports, and then provide recursively
completion support for each command.

Note: by "fake", I mean we use hand-built output and hardcoded
"--help-completion" matching, as opposed to automatically doing it via
regular options. It could be possible in the future to use a
two-staged command line parser, but for now not sure if it's worth it.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Michele Tartara <05f7077a2c6cbbdc4af4ba42e3ef89a0df846179@google.com>

grnet/snf-ganeti,bitemyapp/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,mbakke/ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,dimara/ganeti,ganeti/ganeti,ganeti/ganeti,dimara/ganeti,apyrgio/ganeti,yiannist/ganeti,apyrgio/ganeti,leshchevds/ganeti,andir/ganeti,mbakke/ganeti,yiannist/ganeti,andir/ganeti,onponomarev/ganeti,grnet/snf-ganeti,andir/ganeti,ganeti/ganeti,mbakke/ganeti,yiannist/ganeti,apyrgio/snf-ganeti,apyrgio/snf-ganeti,bitemyapp/ganeti