test: adapt to change in cache warming in core Core Mercurial has a more rational cache warming strategy now. 2b6692df1bdf stopped warming of the cache after every commit (in favor of end of transaction warming). This reflect in the blackbox test output.

stablerangecache: avoid crash when 'cache/' directory is missing If the directory is missing, we create it.

obshashrange: avoid crash when 'cache/' directory is missing If the directory is missing, we create it.