syncbase/bridge/go: Populate the discharges in newFakeServerCall
syncbase/bridge/go: Populate the discharges in newFakeServerCall

The errors we get without this fix look like this:

	rejected blessings: [{"dev.v.io:o:608941808256-43vtfndets79kf5hac8ieujto8837660.apps.googleusercontent.com:razvanm.test.00@gmail.com": gojni: caveat validation failed: gojni:missing discharge for third party caveat(id=Eywl6NfD81tMuG0pK8k0xmLl4RUgMASY6mgaMgGeO7w=)}]

Thanks to mattr for pointing out this fix and to ivanpi for
investigating the issue.

Change-Id: I7e29c1e657333579d1530cf05e010a2ee6bdde4a

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref