MB-9133 Use native index builder for index builds

Just use the new external program in couchstore to do the
initial index builds.

Sample test:

Building an index for a design document with 4 views, from
one of the evperf tests, for a dataset of 6.5M documents:

Before this change:

Total indexing time:    10m58.060s
Btree build phase time: 127.85283s

After this change:

Indexing time:          9m1.305s
Btree build phase time: 22.018846s

Change-Id: Ibec96b74ca219483694ebf71323af921c23dc58e
Reviewed-on: http://review.couchbase.org/29033
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>