mainapp: Parse action -> target mappings on the command line

This adds the argument --action_target=<action>=<systemd_target>.
Depending on the HostAction that is set when the watchdog expires we can
start different systemd targets. The configuration of this mapping is
now configurable at the command line.

Change-Id: I7482e038d9abafc81cec0df15345cbfc670dbed2
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/argument.cpp b/argument.cpp
index edbaa65..f37524e 100644
--- a/argument.cpp
+++ b/argument.cpp
@@ -90,17 +90,19 @@
 {
     std::cerr << "Usage: " << argv[0] << " options\n";
     std::cerr << "Options:\n";
-    std::cerr << " --help                        Print this menu\n";
-    std::cerr << " --path=<Dbus Object path>     Dbus Object path."
-                                                 " Ex: /xyz/openbmc_project/"
-                                                 "state/watchdog/host0\n";
-    std::cerr << " --service=<Dbus Service name> Dbus Service name."
-                                                 " Ex: xyz.openbmc_project."
-                                                 "State.Watchdog.Host\n";
-    std::cerr << " [--target=<systemd unit>]     Systemd unit to be called on"
-                                                 " timeout\n";
-    std::cerr << " [--continue]                  Continue daemon after"
-                                                 " watchdog timeout.\n";
+    std::cerr << " --help                           Print this menu\n";
+    std::cerr << " --path=<Dbus Object path>        Dbus Object path."
+                     " Ex: /xyz/openbmc_project/state/watchdog/host0\n";
+    std::cerr << " --service=<Dbus Service name>    Dbus Service name."
+                     " Ex: xyz.openbmc_project.State.Watchdog.Host\n";
+    std::cerr << " [--target=<systemd unit>]        Systemd unit to be called"
+                     " on timeout for all actions but NONE. Deprecated, use"
+                     "--action_target instead.\n";
+    std::cerr << " [--action_target=<action>=<systemd unit>] Map of action to"
+                     "systemd unit to be called on timeout if that action is"
+                     "set for ExpireAction when the timer expires.\n";
+    std::cerr << " [--continue]                     Continue daemon after"
+                     " watchdog timeout.\n";
 }
 } // namespace watchdog
 } // namespace phosphor