The status messages in cron.php are logged at the debug level, which
makes it difficult to separate them from some of the more trivial
messages that we may want to output - for example, when deleting old
cached files from disk.  It's more helpful to log the status messages
at the info level instead, so that people can add log_debug calls more
freely.

Change-Id: Ibdca949d770b84ff910f7aa6a8446c001ed5bbc6
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>