Change log file name of LXC container to include the part of instance uuid

Extend log file name that will passed to lxc-start by adding part
of instance uuid to keep and ensure log file isolation between old
and new instances which has the same instance name.
move lxc container log files to under the PREFIX/var/log/ganeti/lxc
Merge branch 'topic-improve-lxc-support' into build