fix segfault on lxc-create with bad template name

- change get_template_path() to only return NULL or non-NULL since one of
  the callers was doing a free(-1) which caused the segfault. Handle the
  NULL template case in the lxcapi_create() caller.

- make sure to free(tpath) in the sha1sum_file() failure case

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>