LXC: Create per-instance log files
LXC: Create per-instance log files

This replaces the single global log file with per-instance logs.
The instance log file is not truncated when the instance is started.

Signed-off-by: Balazs Lecz <024c580adbe3324c61e798a30c60cf94ec02e89f@google.com>
Reviewed-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>

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