This should fix errors on build envs, where git tags haven't
been fetched. I.e, Travis-ci does not fetch tags before
building a project, wich results in:
   ---> Running in 0d63a3d28a7a
  fatal: No names found, cannot describe anything.
  fatal: No names found, cannot describe anything.
  make[1]: Entering directory '/criu'

The other way is to fetch tags on `git describe` failure, but
it that way has two cons:
- it will change user's git (and I'm not sure it's right);
- we need not only fetch tags in that case, but also remotes,
  as otherwise it will fail with "fatal: No tags can describe <hash>":
  https://travis-ci.org/0x7f454c46/criu/jobs/133362045#L1748

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>