init: Implement 'exec' command.

(cherry-pick of d05ab3952ec0e38f33a0e80ce6b9eb45b0064ba4.)

Change-Id: Id6d9bb32e51a0ad090ed8240cc505dc45b57b35d
diff --git a/init/keywords.h b/init/keywords.h
index 2d97e5b..7473586 100644
--- a/init/keywords.h
+++ b/init/keywords.h
@@ -8,6 +8,7 @@
 int do_domainname(int nargs, char **args);
 int do_enable(int nargs, char **args);
 int do_exec(int nargs, char **args);
+int do_execonce(int nargs, char **args);
 int do_export(int nargs, char **args);
 int do_hostname(int nargs, char **args);
 int do_ifup(int nargs, char **args);
@@ -59,6 +60,7 @@
     KEYWORD(domainname,  COMMAND, 1, do_domainname)
     KEYWORD(enable,      COMMAND, 1, do_enable)
     KEYWORD(exec,        COMMAND, 1, do_exec)
+    KEYWORD(execonce,    COMMAND, 1, do_execonce)
     KEYWORD(export,      COMMAND, 2, do_export)
     KEYWORD(group,       OPTION,  0, 0)
     KEYWORD(hostname,    COMMAND, 1, do_hostname)