Ignore and warn about attempts to reconfigure static Rock store options.

Ignore and warn about attempts to reconfigure static Rock store options.

Some Rock store options cannot be changed dynamically: path, size, and
max-size.  Before the change, there were no checks during reconfigure
to prevent changing these options.  This may lead to Rock cache
corruption and other bugs.  The patch adds necessary checks to Rock
store code.  If user tries to change an option that cannot be updated
dynamically, a warning is reported and the value is left unchanged.