Fix a race condition on index' doc count retrieval

managers.Indices.get_indices() could fail (and raise a KeyError) upon
reading the 'num_docs' of an index just created. Catching the exception
and setting the 'num_docs' to 0 (which is the actual value) fixes the
problem.
Merge pull request #402 from idlead/master

Fix a race condition on index' doc count retrieval