Use syslog tags for output from child processes

The output from child processes was not including the channel; use the
syslog tag for this purpose.  Indicate the channel via a format prefix.
Extend the handle_syslog function to take these new parameters, and make
the callers call them.

Before:

    Sep 18 23:29:53.963471 Herman user.info supervisord: 2013-09-18 23:29:53,963 WARN Failed to clean up '/tmp/vmstat-stderr---supervisor-oFiLCz.log'
    Sep 18 23:29:53.975359 Herman user.info supervisord: 2013-09-18 23:29:53,966 INFO daemonizing the supervisord process
    Sep 18 23:29:53.975830 Herman user.info supervisord: 2013-09-18 23:29:53,966 INFO supervisord started with pid 15612
    Sep 18 23:29:54.969750 Herman user.info supervisord: 2013-09-18 23:29:54,969 INFO spawned: 'vmstat' with pid 15623
    Sep 18 23:29:54.977120 Herman user.info supervisord: vmstat procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
    Sep 18 23:29:54.977307 Herman user.info supervisord: vmstat  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
    Sep 18 23:29:54.977479 Herman user.info supervisord: vmstat  2  0      0 3992100 262988 2215640    0    0    26    22  122  477  2  1 97  0
    Sep 18 23:29:55.977882 Herman user.info supervisord: vmstat  0  0      0 3992012 262988 2215652    0    0     0     0  680 2443  2  0 98  0
    Sep 18 23:29:55.978157 Herman user.info supervisord: 2013-09-18 23:29:55,977 INFO success: vmstat entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
    Sep 18 23:29:56.978259 Herman user.info supervisord: vmstat  0  0      0 3991888 262988 2215624    0    0     0   116  658 2298  2  1 98  0
    Sep 18 23:29:57.978631 Herman user.info supervisord: vmstat  0  0      0 3991084 262988 2215640    0    0     0     0  716 2681  2  0 98  0
    Sep 18 23:29:58.979017 Herman user.info supervisord: vmstat  0  0      0 3991880 262988 2215640    0    0     0     0  659 2380  2  1 98  0
    Sep 18 23:29:58.979867 Herman user.info supervisord: 2013-09-18 23:29:58,979 INFO exited: vmstat (exit status 0; expected)
    Sep 18 23:30:21.540715 Herman user.info supervisord: 2013-09-18 23:30:21,540 WARN received SIGTERM indicating exit request


After:

    Sep 18 23:30:28.741359 Herman user.info supervisord[15768]: Failed to clean up '/tmp/vmstat-stderr---supervisor-oFiLCz.log'
    Sep 18 23:30:28.752947 Herman user.info supervisord[15771]: daemonizing the supervisord process
    Sep 18 23:30:28.753216 Herman user.info supervisord[15771]: supervisord started with pid 15771
    Sep 18 23:30:29.755550 Herman user.info supervisord[15771]: spawned: 'vmstat' with pid 15782
    Sep 18 23:30:29.766649 Herman user.info vmstat: stdout: procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
    Sep 18 23:30:29.766795 Herman user.info vmstat: stdout:  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
    Sep 18 23:30:29.767606 Herman user.info vmstat: stdout:  1  0      0 3990676 262988 2215920    0    0    25    22  122  478  2  1 97  0
    Sep 18 23:30:30.767446 Herman user.info vmstat: stdout:  0  0      0 3989912 262988 2215920    0    0     0    92  727 5290  1  1 97  1
    Sep 18 23:30:30.767643 Herman user.info supervisord[15771]: success: vmstat entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
    Sep 18 23:30:31.767768 Herman user.info vmstat: stdout:  0  0      0 3990020 262988 2215896    0    0     0     0  624 2007  1  1 99  0
    Sep 18 23:30:32.768116 Herman user.info vmstat: stdout:  0  0      0 3990272 262988 2215904    0    0     0     0  582 2041  1  0 99  0
    Sep 18 23:30:33.767999 Herman user.info vmstat: stdout:  1  0      0 3990456 262988 2215904    0    0     0     0  680 2491  2  1 98  0
    Sep 18 23:30:33.768130 Herman user.info supervisord[15771]: exited: vmstat (exit status 0; expected)

In this example output, syslog is configured to show the priority and facility;
normally this is considered noise and not written.
Make syslog handler pass priority of events through

Previously the level of the alert was only formatted by the non-syslog
handlers; pass it through as the syslog priority.

Now our syslog stream looks like this:

    Sep 18 23:39:03.588720 Herman user.warning supervisord[18161]: Failed to clean up '/tmp/vmstat-stderr---supervisor-Q3tGtz.log'
    Sep 18 23:39:03.600233 Herman user.notice supervisord[18164]: daemonizing the supervisord process
    Sep 18 23:39:03.600682 Herman user.notice supervisord[18164]: supervisord started with pid 18164
    Sep 18 23:39:04.596211 Herman user.notice supervisord[18164]: spawned: 'vmstat' with pid 18175
    Sep 18 23:39:04.603711 Herman user.notice vmstat: stdout: procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
    Sep 18 23:39:04.604265 Herman user.notice vmstat: stdout:  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
    Sep 18 23:39:04.604553 Herman user.notice vmstat: stdout:  3  0      0 3979464 264004 2221996    0    0    24    21  119  470  2  1 97  0
    Sep 18 23:39:05.604561 Herman user.notice vmstat: stdout:  0  0      0 3986896 264004 2214836    0    0     0     0  612 3942  1  0 99  0
    Sep 18 23:39:05.605355 Herman user.notice supervisord[18164]: success: vmstat entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
    Sep 18 23:39:08.605574 Herman user.notice vmstat: stdout:  0  0      0 3985940 264008 2215212    0    0     0     8  598 2064  1  0 99  0
    Sep 18 23:39:08.606140 Herman user.notice supervisord[18164]: exited: vmstat (exit status 0; expected)
    Sep 18 23:39:37.159440 Herman user.warning supervisord[18164]: received SIGTERM indicating exit request
Document and changelog syslog enhancements