golang: Run all select tests "more thoroughly"

Starting from b51b8d5d (select: Run tests more thoroughly) we are
running select subtests in repeated mode with N=1000. However not all
select subtests were run in repeated mode - for example e.g.
"non-blocking try send: not ok" was being run only once.

-> Rework all select subtests to be run in repeated mode to increase the
probability of catching bugs.

golang/golang_test.py

@@ -207,6 +207,7 @@ def test_select():
 
     # non-blocking try send: not ok
     ch = chan()
+    for i in range(N):
         _, _rx = select(
                 (ch.send, 0),
                 default,
@@ -214,6 +215,7 @@ def test_select():
         assert (_, _rx) == (1, None)
 
     # non-blocking try recv: not ok
+    for i in range(N):
         _, _rx = select(
                 ch.recv,
                 default,
@@ -281,16 +283,22 @@ def test_select():
     ch2 = chan()
     done = chan()
     def _():
+        while 1:
             waitBlocked(ch1.send)
-        assert ch1.recv() == 'a'
+            x = ch1.recv()
+            if x == 'stop':
+                break
+            assert x == 'a'
         done.close()
     go(_)
 
+    for i in range(N):
         _, _rx = select(
             (ch1.send, 'a'),
             (ch2.send, 'b'),
         )
         assert (_, _rx) == (0, None)
+    ch1.send('stop')
     done.recv()
     assert len_sendq(ch1) == len_recvq(ch1) == 0
     assert len_sendq(ch2) == len_recvq(ch2) == 0
@@ -301,11 +309,13 @@ def test_select():
     ch2 = chan()
     done = chan()
     def _():
+        for i in range(N):
             waitBlocked(ch1.recv)
             ch1.send('a')
         done.close()
     go(_)
 
+    for i in range(N):
         _, _rx = select(
             ch1.recv,
             ch2.recv,
@@ -321,16 +331,22 @@ def test_select():
     ch2 = chan()
     done = chan()
     def _():
+        while 1:
             waitBlocked(ch1.send)
-        assert ch1.recv() == 'a'
+            x = ch1.recv()
+            if x == 'stop':
+                break
+            assert x == 'a'
         done.close()
     go(_)
 
+    for i in range(N):
         _, _rx = select(
             (ch1.send, 'a'),
             ch2.recv,
         )
         assert (_, _rx) == (0, None)
+    ch1.send('stop')
     done.recv()
     assert len_sendq(ch1) == len_recvq(ch1) == 0
     assert len_sendq(ch2) == len_recvq(ch2) == 0
@@ -341,11 +357,13 @@ def test_select():
     ch2 = chan()
     done = chan()
     def _():
+        for i in range(N):
             waitBlocked(ch1.recv)
             ch1.send('a')
         done.close()
     go(_)
 
+    for i in range(N):
         _, _rx = select(
             ch1.recv,
             (ch2.send, 'b'),