Use a custom TrustedCertificateStore

Providing a TrustedCertificateStore to TrustManagerImpl avoids loading
all of the trusted certificates into memory and indexing them. This
is mainly for the system certificate store where loading all of the
store into memory is wasteful for most applications.

Change-Id: I9e6057f6a13d38ea7762fcac2f62bd3ff475af39