The schema distribution data maintained for keeping track of subscribers
assumes that max number of data nodes will never exceed 256.
This is both a limitation in terms of max number of supported data nodes
as well as unnecessary memory usage when using less than 256 data nodes.

Fix by dimensioning the subscriber bitmaps to match the number of
data nodes in configuration. Store the allocated bitmaps in a list which
allows direct lookup from data node id to subscriber bitmap.
Remove the fixed size lookup table from data node id to
subscriber bitmap.
Change the number of subscribers in the bitmap to be dynamically
configurable to allow later adjusting of subscriber size to the
actual maximum subscriber number in the current configuration. Initially
use the compile time constant MAX_NODES.
Add ndb_bitmap_to_hex_string() for printing MY_BITMAP as string, the new
implementation prints the whole bitmap and not only the first two words.
Improve code encapsulation and function comments.

Change-Id: I69b93add7cf2bbe875c32d14e53249a89182db71