Fix verify script

No longer pulling a separate copy of Yokozuna. Just use one in Riak
deps.
Change index exists check to use on-disk information

Add a function to get the lists of indexes created on disk. When
determining if an index exists use this information rather than a ping
request. This is more reliable because a ping request will fail if Solr
is down but the index actually exists. That causes unnecessary
error messages because Yokozuna will try to re-create indexes when
they already exist while Solr is down.
Change index exists to check 3 conditions for existence

It's not enough to just check that the index is in the official list and
exist on disk. The index might have a bad schema which keeps it from
starting. Without this patch the schema admin test will fail for just
that reason.

When Solr is up then the index should meet all three conditions below.
When Solr is down only the first two conditions must be met to be
considered as existing.

1. The index is in the "official list" (currently stored in ring).

2. The index has a dir under root data dir.

3. The index can be pinged via HTTP.
Merge pull request #274 from basho/bugfix/rz/better-index-exists

Better index exists.