This test was using a sleep of 1 second in an attempt to ensure that the
timestamp that is part of an InnoDB status string would increase.
This not only prolongs the test execution time by 1+1 seconds, but it
also is inaccurate. It is possible that the actual sleep duration is
less than a second.
Let us wait for the creation of the file ib_buffer_pool and then wait
for the buffer pool dump completion. In that way, the test can complete
in a dozen or two milliseconds (1% of the previous duration) and work
more reliably.
Let us make innodb_buffer_pool_filename a read-only variable
so that a malicious user cannot cause an important file to be
deleted on InnoDB shutdown. An attempt to delete a directory
will fail because it is not a regular file, but what if the
variable pointed to (say) ibdata1, ib_logfile0 or some *.ibd file?
It does not seem to make much sense for this parameter to be
configurable in the first place, but we will not change that in order
to avoid breaking compatibility.
