pulp-manage-db drops and rebuilds all indices every run
Description of problem:
Every time pulp-manage-db is run, it drops all DB indices and rebuilds them. This is very inefficient.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Run pulp-manage-db on a Pulp installation with data (repos with units, for example).
Observe that it takes a while before applying migrations.
There is no need to drop indices that we are going to just regenerate.
If we switch to Mongoengine, it will take care of index management for us.
+ This bug was cloned from Bugzilla Bug #1134021 +