A couple of small changes to the OS environment
A couple of small changes to the OS environment

This patch correctly exports the mode of disks (rw/ro) and also exports
the instance OS.

Reviewed-by: imsnah

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