This commit adds the ability to force blocking on the flush operaition
to make sure all files have been written and synced to disk. Without
this option a flush might be executing at the same time causing the
current flush to fail and return before all files being synced.
Closes#6996
* `ignore_unavailable` - Controls whether to ignore if any specified indices are unavailable, this includes indices that don't exist or closed indices. Either `true` or `false` can be specified.
* `allow_no_indices` - Controls whether to fail if a wildcard indices expressions results into no concrete indices. Either `true` or `false` can be specified. For example if the wildcard expression `foo*` is specified and no indices are available that start with `foo` then depending on this setting the request will fail. This setting is also applicable when `_all`, `*` or no index has been specified.
* `expand_wildcards` - Controls to what kind of concrete indices wildcard indices expression expand to. If `open` is specified then the wildcard expression if expanded to only open indices and if `closed` is specified then the wildcard expression if expanded only to closed indices. Also both values (`open,closed`) can be specified to expand to all indices.
Closes to #4436
Files were generated with the `thor api:generate:spec --force --verbose --crawl` command,
and based on the 0.90 branch (elasticsearch/elasticsearch@5ec4064).
Simon Willnauer
Clinton Gormley
Spencer Alger
Martijn van Groningen
Honza Kral
Karel Minarik