tests/thread: Remove need to sleep to wait for completion in some tests.

Use a lock and a counter instead, and busy wait for all threads to
complete.  This makes test run faster and they no longer rely on the time
module.

tests/thread/thread_stacksize1.py

@@ -3,10 +3,6 @@
 # MIT license; Copyright (c) 2016 Damien P. George on behalf of Pycom Ltd
 
 import sys
-try:
-    import utime as time
-except ImportError:
-    import time
 import _thread
 
 # different implementations have different minimum sizes
@@ -20,6 +16,9 @@ def foo():
 
 def thread_entry():
     foo()
+    with lock:
+        global n_finished
+        n_finished += 1
 
 # test set/get of stack size
 print(_thread.stack_size())
@@ -27,10 +26,16 @@ print(_thread.stack_size(sz))
 print(_thread.stack_size() == sz)
 print(_thread.stack_size())
 
+lock = _thread.allocate_lock()
+n_thread = 2
+n_finished = 0
+
 # set stack size and spawn a few threads
 _thread.stack_size(sz)
-for i in range(2):
+for i in range(n_thread):
     _thread.start_new_thread(thread_entry, ())
 
-time.sleep(0.2)
+# busy wait for threads to finish
+while n_finished < n_thread:
+    pass
 print('done')