LU-9727 nodemap: add audit_mode flag to nodemap

LU-9727 nodemap: add audit_mode flag to nodemap

Give the ability to specify an audit_mode flag on a nodemap.
When set to 1, a client pertaining to this nodemap will be able to
record file system access events to the Changelogs, if Changelogs are
otherwise activated.
When set to 0, events are not logged into the Changelogs, no matter
Changelogs are activated or not.
By default, audit_mode flag is set to 1 in newly created nodemap
entries. And it is also set to 1 on 'default' nodemap.

The idea of disabling audit on a per-nodemap basis is that it would
be possible to have some nodes (e.g. backup, HSM agent nodes) that do
not flood the audit logs.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Ieb6c461c443b1734312afef44680d903deee5398
Reviewed-on: https://review.whamcloud.com/28313
Reviewed-by: Jean-Baptiste Riaux <riaux.jb@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>