Add myself to Keystore owners

Update the Keystore owners file:
* Remove Rob Barnes
* Add myself.

This will remove the dependency on US-based reviewers for all Keystore
Java CLs.
Non-trivial CLs, CLs that are not strictly in the Java layer, or both,
would still be sent to the right US-based reviewer.

Bug: N/A
Test: N/A
Change-Id: Id8931516b90be4b97e684cb8d7f9de8d71643db4