binder: implement simple TLS verification for testing

Implements RpcCertificateVerifierSimple with an algorithm
that treats all certificates as leaf certificates.

Fix existing tests to set certificates properly. Also
add a test that checks that bad certificates are rejected.

Also adds RpcCertificateUtils that includes function for
(de)serializing certificates. These util functions are useful
for implementing RpcCertificateVerifier.

Test: binderRpcTest
Bug: 195166979
Fixes: 196422181
Fixes: 198833574
Change-Id: I6c1f0f88fe5bc712f3890426d6da26c9ad046d79