Rather than innodb_buffer_pool_dump_pct referring to the percentage of hot data
in the buffer pool, it refers to the entire buffer pool size. This means that a
completed load followed by a shutdown will write the exact same data.

The problem was:

With innodb_buffer_pool_dump_pct say 25% (the default since 10.2.2), a server
started will restore 25% of the buffer pool size with the expectation that over
time the rest of the buffer pool will be populated. Then on shutdown 25% will
be saved.

If a server is started and then is shutdown a) without much activity occurring
b) is started as a hot spare and shutdown before being used, then 6.25% (25%
of 25%) of the buffer pool is saved.

This will generate bigger dump files for users who don't have a full
innodb_buffer_pool however a realistic scenario is a buffer pool should be
completely used.
Signed-off-by: Daniel Black <daniel.black@au.ibm.com>