Do not crash if view group already defined when ddoc changes.
Do not crash if view group already defined when ddoc changes.

It's possible that the design document has the same value as it used
to have previously. Then view group can already be defined.

Change-Id: Icbd9b516d68c754fc30fba7b56f305956f9e144d
Reviewed-on: http://review.couchbase.org/12091
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Srinivas Vadlamani <4036f57732a648e71da3ac2c829c8239a16a4c5d@couchbase.com>

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