Running tests with USE_LDAP enabled outside of Yale breaks things

[orenyk]

While waiting for my car to get serviced and trying to get work done, I encountered a bunch of failed tests due to LDAP lookup timeouts as I had USE_LDAP set from a different issue (#1375). I'll verify that everything passes when LDAP is disabled, but we should probably enforce ENV['USE_LDAP'] = nil for the test environment. If we really wanted to do things right, we'd also go through and either remove all tests that are directly related to LDAP and/or stub LDAP queries somehow.

Here are the tests that failed before I killed Rspec (was taking forever):

• spec/controllers/users_controller_spec.rb:59
• spec/controllers/import_users_controller.rb (a bunch)

Let's do it right:

• ensure USE_LDAP defaults to nil in test
• properly stub LDAP queries and run them in isolated blocks with ENV modified
• go through all LDAP-related specs and make sure they're actually worth testing