Stop leaking identity resources in teardown_all()

teardown_all() tries to delete all resources. But if an exception
happens, the rest of resources are remained and it seems to happen
frequently.
This commit fixes it.

Partially Implements: blueprint stop-leaking
Change-Id: I671b2262ea5ed5bf7d78149cf88f2894b6bf6508
Merge "Stop leaking identity resources in teardown_all()"