testsuite: add kvs-watch-until.lua

Add the kvs-watch-until.lua helper script from flux-core to
t/scripts in flux-sched.

t/scripts/kvs-watch-until.lua

@@ -0,0 +1,84 @@
+#!/usr/bin/env lua
+--
+--  Exit only if/when all ranks have exited 'unknown' state
+--
+local usage = [[
+Usage: kvs-wait-until [OPTIONS] KEY CODE
+
+Watch kvs KEY until Lua code CODE returns true.
+(CODE is supplied key value in variable 'v')
+If -t, --timeout is provided, and the timeout expires, then
+exit with non-zero exit status.
+
+ -h, --help       Display this message
+ -v, --verbose    Print value on each watch callback
+ -t, --timeout=T  Wait at most T seconds (before exiting
+]]
+
+local getopt = require 'flux.alt_getopt' .get_opts
+local timer =  require 'flux.timer'.new()
+local f =      require 'flux' .new()
+
+local function printf (...)
+    io.stdout:write (string.format (...))
+end
+local function log_err (...)
+    io.stdout:write (string.format (...))
+end
+
+local opts, optind = getopt (arg, "hvt:",
+                             { verbose = 'v',
+                               timeout = 't',
+                               help = 'h'
+                             }
+                            )
+if opts.h then print (usage); os.exit (0) end
+
+local key = arg [optind]
+local callback = arg [optind+1]
+
+if not key or not callback then
+    log_err ("KVS key and callback code required\n")
+    print (usage)
+    os.exit (1)
+end
+
+callback = "return function (v)  return "..callback.." end"
+local fn, err = loadstring (callback, "callback")
+if not fn then
+    log_err ("code compile error: %s", err)
+    os.exit (1)
+end
+local cb = fn ()
+
+local kw, err = f:kvswatcher {
+    key = key,
+    handler = function (kw, result)
+        if opts.v then
+            printf ("%4.03fs: %s = %s\n",
+                    timer:get0(),
+                    key, tostring (result))
+        end
+        -- Do not pass nil result to callback:
+        if result == nil then return end
+        local ok, rv = pcall (cb, result)
+        if not ok then error (rv) end
+        if ok and rv then
+            os.exit (0)
+        end
+    end
+}
+
+if opts.t then
+    local tw, err = f:timer {
+        timeout = opts.t * 1000,
+        handler = function (f, to)
+               log_err ("%4.03fs: Timeout expired!\n", timer:get0())
+               os.exit (1)
+        end
+    }
+end
+
+timer:set ()
+f:reactor ()
+-- vi: ts=4 sw=4 expandtab