Remove log_dir from params and make logs configurable in init

log_dir does not seem to be used in other classes. In the use case where
it can be necessary to specify the location of ceilometer logs, this
patch makes it possible to do so while maintaining the default for
backwards compatibility. This patch also adds the possibility of
sending logs to syslog/rsyslog in the same way as implemented in
puppet-nova.

Change-Id: I1f970d5e3cc947308221fb2b2cdfb34f89c64314
Partial-Bug: #1269482