MB-7248 enforce maximum number of buckets

...during sample buckets creation

- re-factored sample loading code to use the same stack as normal bucket creation
- improved error handling of the sample buckets creation API
- enforced max number of buckets on the UI level

Change-Id: I3fe28542ac052a39a9f8aa46e442ee82f0e1c435
Reviewed-on: http://review.couchbase.org/27432
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-8598 - fix for alerts UI and REST API

- fixed typo in UI code that messes up
  "Writing data to disk for a specific bucket has failed" alert
- changed REST API so it will error out if
  the unsupported paramater is passed

Change-Id: I25d5609f25b6e414dcb2591c99da38ccd8774b9e
Reviewed-on: http://review.couchbase.org/27453
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>