Fix gnt-instance start/stop/… args
Fix gnt-instance start/stop/… args

The gnt-instance commands that have the multi-filter can take also zero
arguments, if the --all flag is passed. But they currently are declared
with min=1, and this is a regression due to the recent bash completion
changes.

There is also the problem that --primary/--secondary expect a node and
not an instance, but currently the completion doesn't support this
distinction.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>

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