only care about set index indexing and compaction
only care about set index indexing and compaction

When usual couch index is being updated or compacted it's causing our
tasks progress aggregation code to crash because there are no expected
fields such as set or design_documents.

Seen in MB-4741. But main cause of MB-4741 is seemingly erlang vm
crash.

Change-Id: Icaf2a183b4433119b2d293bb193df9b97cc24877
Reviewed-on: http://review.couchbase.org/12902
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

pavel-blagodov/ns_server,pavel-blagodov/ns_server,vzasade/ns_server,nimishzynga/ns_server,pavel-blagodov/ns_server,nimishzynga/ns_server,vzasade/ns_server,mschoch/ns_server,daverigby/ns_server,mschoch/ns_server,membase/ns_server,daverigby/ns_server,vzasade/ns_server,vzasade/ns_server,t3rm1n4l/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,mschoch/ns_server,membase/ns_server,t3rm1n4l/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,mschoch/ns_server,daverigby/ns_server,ceejatec/ns_server,daverigby/ns_server,nimishzynga/ns_server,daverigby/ns_server,membase/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,membase/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server