couchbase-cli pump rehash only works for powers of two number of vbuckets

Modulo should be used to convert a crc32 hash into a lower range of mappings (e.g. from the full 32bit range to 1024). The way the couchbase-cli pump currently does it is by subtracting 1 from the number of vbuckets (e.g. to 1023 == 0x3FF or the lower 10bits as 1) and using that as a bitmask.

While this works for powers of 2 like 64 and 1024 it does not work for others like 61. The couchbase-cli pump should just use Python's modulo operator instead of a bitmask.