MB-11717: validate cluster-wide collectinfo customer and ticket

Somehow I haven't spotted that spec required us to validate them.

Per spec we validate customer to be [A-Za-z0-9._ -] and at most 50
chars. And we validate ticket to be numeric and at most 7 chars.

Change-Id: Idbd025e81f618101c64f5d9e46c54dcbaa508554
Reviewed-on: http://review.couchbase.org/39363
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>