Revert "Delete obsolete and unused KeyStoreTests". DO NOT MERGE ANYWHERE.

Needed to revert the CL's base CL, which tracks the revert
of the corrsponding conscrypt CL.

This reverts commit 91abf9f6.

This is a clean revert. The upload hook to fix lint errors was not run
(this CL was uploaded with --no-verify).

Test: Treehugger
Test: make droid cts
Bug: 62424503

Change-Id: Ic7a3a5550b1e2bdfec98acd986a6a4e84eef41ea