Added waiting for yellow cluster state in rest test

In order to prevent rare timing issue, where the creation
of an index happens in the cluster state too late and thus
results in empty mappings.
Don't fail plugin manager test when downloading an actual plugin
[DOCS] Added breaking changes in 1.0
[DOCS] Fixed asciidoc issue
release [1.0.0.RC1]
[DOCS] Minor changes to the breaking changes doc
[DOCS] Add documentation for URL repository
Added note to release script to announce on ML
Fixed test bug, was using value that wasn't generated.
move to [1.0.0] SNAP
[DOCS] made it clearer that the _version is incremented by all write operations (deletes included)
[DOCS] updated json responses after #4310 and #4480

 - Removed "ok": true from response examples
 - Added "created" flag to index response examples
 - Replaced exists flag with found in delete response examples
[DOCS] Tidied up asciidoc for migration page
[SPEC] Added human flag to:
* cluster.node_info
* cluster.node_stats
* indices.segments
* indices.stats
* indices.status
[DOCS] Fixed typo in frontends.asciidoc
[SPEC] Added the routing and timeout params to bulk
[SPEC] Added cat.json
[SPEC] Added cluster.repositories.* and cluster.snapshots.*
[SPEC] Added cluster.stats.json
[SPEC] Added cluster.pending_tasks.json