Propagate cancellation to spawned test jobs

A user might cancel test result in ERP5 UI if e.g. some misbehaviour is
detected and a new revision is ready to be tested. This works by
test_result.start() returning None - indicating that there is no more
test_result_lines to exercise. Master also indicates this cancellation
via test_result.isAlive() returning False, but until now we were not
using that information and were always waiting for completion of current
test job that is already spawned.

This works well in practice if individual tests are not long, but e.g.
for SlapOS.SoftwareReleases.IntegrationTest-* it is not good, because
there an individual test might takes _hours_ to execute.

-> Fix it by first setting global context to where we'll propagate
cancellation from test_result.isAlive, and by using that context as the
base for all other activities. This should terminate spawned test
process if test_result is canceled.

The interval to check is picked up as 5 minutes not to overload master.
@jerome says that

    We now have 341 active test nodes, but sometimes we are using
    more, we did in the past to stress test some new machines.

    For the developer, if we reduce the waiting time from a few hours to 1
    minutes or 5 minutes seems more or less equivalent.

For 350 testnodes and each nxdtest checking its test_result status via
isAlive query to master every 5 minutes, it results in ~ 1 isAlive
request/second to master on average.

Had to change time to golang.time to use time.after().
Due to that time() and sleep() are changed to time.now() and
time.sleep() correspondingly.

/helped-by @jerome

nxdtest/__init__.py

@@ -57,12 +57,12 @@ from __future__ import print_function, absolute_import
 
 from erp5.util.taskdistribution import TaskDistributor
 from subprocess import Popen, PIPE
-from time import time, sleep, strftime, gmtime, localtime
+from time import strftime, gmtime, localtime
 import os, sys, argparse, logging, traceback, re, pwd, socket
 from errno import ESRCH, EPERM
 import six
 from golang import b, defer, func, select, default
-from golang import errors, context, sync
+from golang import errors, context, sync, time
 import psutil
 
 # loadNXDTestFile loads .nxdtest file located @path.
@@ -211,6 +211,28 @@ def main():
       bstdout = sys.stdout.buffer
       bstderr = sys.stderr.buffer
 
+    # setup context that is canceled when/if test_result is canceled on master
+    # we will use this context as the base for all spawned jobs
+    ctx, cancel = context.with_cancel(context.background())
+    cancelWG = sync.WorkGroup(ctx)
+    @func
+    def _(ctx):
+        defer(cancel)
+        while 1:
+            _, _rx = select(
+                    ctx.done().recv,                # 0
+                    time.after(5*time.minute).recv, # 1   NOTE not e.g. one second not to overload master
+            )
+            if _ == 0:
+                break
+
+            if not test_result.isAlive():
+                emit("# master asks to cancel test run")
+                break
+    cancelWG.go(_)
+    defer(cancelWG.wait)
+    defer(cancel)
+
     # run the tests
     devnull = open(os.devnull)
     while 1:
@@ -225,7 +247,7 @@ def main():
 
         # run tenv[name]
         t = tenv.byname[test_result_line.name]
-        tstart = time()
+        tstart = time.now()
 
         emit('\n>>> %s' % t.name)
         emit('$ %s' % t.command_str())
@@ -263,7 +285,7 @@ def main():
             # (explicit teeing instead of p.communicate() to be able to see incremental progress)
             buf_out = []
             buf_err = []
-            wg = sync.WorkGroup(context.background())
+            wg = sync.WorkGroup(ctx)
             wg.go(tee, p.stdout, bstdout, buf_out)
             wg.go(tee, p.stderr, bstderr, buf_err)
             # wait for p to exit
@@ -285,7 +307,7 @@ def main():
                         err = ctx.err()
                         break
 
-                    sleep(0.1)
+                    time.sleep(0.1)
 
                 # p should be done - check if it leaked processes and terminate/kill them
                 # kill p in the end if it does not stop from just SIGTERM.
@@ -333,7 +355,7 @@ def main():
                     status.update(summary)
 
 
-        tend = time()
+        tend = time.now()
 
         # print summary and report result of test run back to master
         tres = {
@@ -465,6 +487,9 @@ class LocalTestResult:
             test_result_line.name = t.name
             return test_result_line
 
+    def isAlive(self): # -> bool (whether still running)
+        return True # don't need to handle SIGINT - CTRL+C interrupts whole process
+
 class LocalTestResultLine:
     def stop(self, **kw):
         # XXX + dump .json ?