extracted multicall_ignoring_undefined. MB-5118
extracted multicall_ignoring_undefined. MB-5118

We're going to use it in next patch

Change-Id: I17909b96089fe1f0749b7d8694dd3ee722ead082
Reviewed-on: http://review.couchbase.org/15053
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

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