keycache: restructure functions that are controlled by arguements

finish_resize_simple_key_cache removed argument acquire for acquiring
locks.

resize_simple_key_cache enforces assertion that the cache is inited.

read_block was really two functions, primary and secondary so separated
as such. Make the callers of read_block explictly use the required function.
Signed-off-by: Daniel Black <daniel@linux.vnet.ibm.com>