Use WatchedFileHandler instead of RotatingFileHandler

Even though we just switched to RotatingFileHandler, it does not
interact well with logrotate, whereas WatchedFileHandler is
explicitly intended to deal with that use case. Additionally,
using WatchedFileHandler ensures that the logging page accurately
reflects the actual sizes of logfiles, and that our own logrotate
job performs as expected.

Change-Id: I6230b1da121a8c3711b7c09cbc8b174ee6b12032
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=976053
Signed-off-by: Ryan Barry <rbarry@redhat.com>