Major change, rename <svc/...> conditions to <pid/...> conditions

The <svc/foo> condition was created to synchronize starting services,
hence the abbreviation.  Example: the Quagga ripd needs to start after
the zebra daemon to ensure its UNIX domain socket is active, otherwise
events may be lost.

However, considering that synchronization was implemented with UNIX PID
files, e.g. waiting for /var/run/quagga/zebra.pid to be created, the
condition abbreviation name <svc/foo> was hard to understand by most
newcomers to Finit.  To make matters worse, a new feature to track or
even create PID files for services that don't create one themselves,
using the syntax 'pid:/path/to/foo.pid' was added.

Connecting the dots between these wasn't obvious.

This patch renames service conditions pid conditions and also adds
a compatibility wrapper to the Finit .conf parser.  Any condition
given in old .conf files with 'svc/' prefix are internally renamed
'pid/', along with a LOG_INFO notice in syslog.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/conditions.md

@@ -31,11 +31,11 @@ service to run.
 ### Example
 
 ```shell
-    service [2345] <svc/sbin/setupd,svc/sbin/zebra> /sbin/netd -- Network monitor
+    service [2345] <pid/sbin/setupd,pid/sbin/zebra> /sbin/netd -- Network monitor
 ```
 
 In this example the Network monitor daemon `netd` is not started until
-both the `svc/sbin/setupd` *and* `svc/sbin/zebra` conditions are
+both the `pid/sbin/setupd` *and* `pid/sbin/zebra` conditions are
 satisfied.  An `svc` condition is satisfied by the corresponding
 service's PID file being created.
 
@@ -62,7 +62,7 @@ Built-in Conditions
 
 Finit is distributed with a `pidfile` and `netlink` plugin.  If enabled,
 the `pidfile` plugin watches `/var/run/` for PID files created by the
-monitored services, and sets a corresponding condition in the `svc/`
+monitored services, and sets a corresponding condition in the `pid/`
 namespace.  Similarily, the `netlink` plugin provides basic conditions
 for when an interface is brought up/down and when a default route
 (gateway) is set, in the `net/` namespace.
@@ -81,7 +81,7 @@ file touched (re-created).
 
 Built-in conditions:
 
-- `svc/<PATH>`
+- `pid/<PATH>`
 - `net/route/default`
 - `net/<IFNAME>/exist`
 - `net/<IFNAME>/up`
@@ -95,16 +95,16 @@ Built-in conditions:
 Composition
 -----------
 
-The `svc/` conditions can be quite tricky to understand.  They are
+The `pid/` conditions can be quite tricky to understand.  They are
 generated by the Finit `pidfile.so` plugin and are composed from the
 daemon's path and the pidfile name (and path).
 
 | **service**                          | **pid:**        | **pidfile path** | **svc condition** |
 |--------------------------------------|-----------------|------------------|-------------------|
-| /sbin/foo                            |                 | /run/foo.pid     | svc/sbin/foo      |
-| /sbin/bar -p /run/baz.pid            | pid:baz         | /run/bas.pid     | svc/sbin/baz      |
-| lxc-start -n foo -p /run/lxc/foo.pid | pid:lxc/foo.pid | /run/lxc/foo.pid | svc/lxc/foo       |
-| /usr/bin/dbus-daemon                 | pid:dbus/pid    | /run/dbus/pid    | svc/usr/bin/dbus  |
+| /sbin/foo                            |                 | /run/foo.pid     | pid/sbin/foo      |
+| /sbin/bar -p /run/baz.pid            | pid:baz         | /run/bas.pid     | pid/sbin/baz      |
+| lxc-start -n foo -p /run/lxc/foo.pid | pid:lxc/foo.pid | /run/lxc/foo.pid | pid/lxc/foo       |
+| /usr/bin/dbus-daemon                 | pid:dbus/pid    | /run/dbus/pid    | pid/usr/bin/dbus  |
 
 Omitting the `pid:` to run/task/service/sysv stanza means Finit will
 guess the pidfile path based on `/run/` and the basename(1) of the
@@ -128,7 +128,7 @@ conditions that are not satisfied.  Listed as `off` below.
     ~ # initctl cond show
     PID     Service               Status  Condition (+ on, ~ flux, - off)
     ===============================================================================
-    1419    /sbin/netd            on      <+svc/sbin/setupd,+svc/sbin/zebra>
+    1419    /sbin/netd            on      <+pid/sbin/setupd,+pid/sbin/zebra>
     0       /sbin/udhcpc          off     <-net/vlan1/exist>
 ```