Add AOSP certificates for connectivity resources

Instead of the platform certificate, use a dedicated certificate.

The AOSP certificates are only used for testing as they have known keys,
and are replaced when resigning production images.

Key generated with:
openssl req -x509 -newkey rsa:4096 -nodes -days 999999 -keyout key.pem \
    -out com.android.connectivity.resources.x509.pem
openssl pkcs8 -topk8 -inform PEM -outform DER -in key.pem -out \
    com.android.connectivity.resources.pk8 -nocrypt

Fixes: 184808224
Fixes: 185462051
Test: m
Change-Id: I25cddc8d5ab948da9d3a2dbcd202ece1f61dd5a2