Idempotent APIs for partially active feed.

Previously projector was shutting down all vbuckets (including successfully)
started once, when everh ErrorResponseTimeout happens. This is changed
to keep the feed active with partial set of vbuckets and expect repeated
calls from coordinator / indexer until the feed is fully stable.

More information on the API can be gathered by referring to
projector/client/client.go

- added book-keeping for partially active feed.
- ErrorFeeder to denote upstream connection error, in which case the bucket
  is shutdown and its data-structures are cleanedup.
- updated multibucket script to restart from previous cut-off.
- interpret STREAM_REQUEST and STREAM_END for error status.

Change-Id: I8f9ca58c46ed36c945a0f96d7eba6bb456b39dd6
Reviewed-on: http://review.couchbase.org/43072
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>