Don't query for object's memberships when reindexing

It doesn't make sense to query for memberships, since we're not indexing
them anyway (see e45b8b2). The memberships in elasticsearch are indexed
to contain the person and organization they relate to, so that's the
best place to query them anyway.
Increase timeout to 10 minutes

This is working around the problem of slow reindexing, rather than
putting in a proper fix, but for the time being this seems to be the
easiest way to solve this problem.