Add capability to use syslog for logging

This patch adds a configure-time parameter that will set the defaults
used by all programs, and command-line parameters in the daemons that
allow overriding it.

Syslog 'yes' enables syslog in addition to file-based logging, 'only'
enables syslog and disables file-based syslog.

The log entries will be of the form:
Jan 27 08:45:04 node2 ganeti-noded[14504]: INFO 172.24.227.5:50850 PUT
/jobqueue_update HTTP/1.0 200
Jan 27 08:45:05 node2 ganeti-noded[14505]: INFO 172.24.227.5:50853 PUT
/lv_list HTTP/1.0 200

and (for a multi-threaded program):
Jan 27 08:51:48 node1 ganeti-masterd[15491]: (MainThread) INFO
ganeti-masterd daemon startup
Jan 27 08:51:49 node1 ganeti-masterd[15491]: (MainThread) INFO
Inspecting job queue

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>