crash_reporter: Use cacerts_google

Use /system/etc/security/cacerts_google as the default certificates
directory.  If the crash_reporter.full_certs property is set to 1,
use the full /system/etc/security/cacerts directory.  This
property can be set in a target's product.mk, if they decide to
configure crash_reporter with a crash_server not covered by the
cacerts_google subset of certificates.

Bug: 25798318
Change-Id: I617c3d13b74af8d9577823a8f1a61f8375bcb504