The proxy server on occasion has error limited a node by the time the
test runs, causing the proxie's node_iter failing to iter out this
error limited node. As the test uses a default FakeRing with no
extra handoffs, on this occasion we only get 2 requests which is not
enough for quorum, causing it to return a 503.
This patch sets the error_suppression_interval to 0 when creating
the proxy server. Meaning a node effectively isn't error_limited.
Change-Id: I96cf4c4d63594f803cc1cd57e874d1624db8e249
Closes-Bug: #1682026