Allow specifying journal_dir for rrdcached

Turns out we want to put it under /srv since it has the tendency to grow
a lot. Also pass the -F flag so that on shutdown everything is flushed
While at it, have puppet notify rrdcached/gmetad on configuration file
changes

Change-Id: I515ac8f116890159d5c416aacab5c2ba2b99aca6
Merge "Allow specifying journal_dir for rrdcached" into production