Add an atomic ConfigWrite.GetAllInstanceInfo()
Add an atomic ConfigWrite.GetAllInstanceInfo()

In order to be able to query instance without locking them, we need the
same atomic query of multiple instances as for nodes.

Reviewed-by: ultrotter


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