As collections has moved to collections.abc, this produces a warning which may lead to unit testing errors: this is the case when building Rally.
This patch attempts to import from collections.abc, and if it fails, falls back to collections. This should be harmless.
Note that this patch is probably useless with future version, as hopefully, upstream will fix it (I didn't check). However, I didn't dare upgrading the package to the major upstream release 3.x.
