Create OS from an InvalidOS error
Create OS from an InvalidOS error

Add a new FromInvalidOS static function to objects.OS that makes it easy to
create an object representing a broken OS starting from the relevant exception.

Reviewed-By: iustinp



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