Sync addRegionParent: no more store snapshot. Results:

(issue #116)

Running with /usr/bin/time --verbose we get a decrease
of 2.5 in Maximum Resident Size memory.

Profiling give us a decrease in alloc_space from ~90%
to below 50%. See profiling results:

NEW
Showing top 10 nodes out of 292 (cum >= 2.51MB)
      flat  flat%   sum%        cum   cum%
   20.87MB 20.87% 20.87%    20.87MB 20.87%  runtime.makemap
   12.50MB 12.51% 33.38%    48.87MB 48.88%  github.com/wallix/awless/vendor/github.com/wallix/triplestore.(*source).Snapshot
   11.50MB 11.50% 44.88%    11.50MB 11.50%  runtime.rawstringtmp

OLD
Showing top 10 nodes out of 80 (cum >= 2MB)
      flat  flat%   sum%        cum   cum%
  165.34MB 46.51% 46.51%   165.34MB 46.51%  runtime.makemap
   80.51MB 22.65% 69.16%    80.51MB 22.65%  runtime.rawstringtmp
   55.54MB 15.62% 84.78%   323.87MB 91.10%  github.com/wallix/awless/vendor/github.com/wallix/triplestore.(*source).Snapshot