1. If no template is passed in, then do not try to execute it.  The user
just wanted to write the configuration.

2. If template is passed in as a full path, then use that instead of
constructing '$templatedir/lxc-$template'.
Reported-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>