Fix some random deadlock while running fedabipkgidiff in tests

We are seeing some random cases where the regression test
runtestfedabipkgdiff.py hangs in what seems to be a deadlock.  This
seems to happen in fedabipkgidiff when it spawns a process to run
abipkgdiff.  More precisely, proc.communicate() hangs.

The documentation of that function at
https://docs.python.org/2/library/subprocess.html#subprocess.Popen.communicate
says:

    Note: The data read is buffered in memory, so do not use this
    method if the data size is large or unlimited.

So this patch avoids using proc.communicate() because the output of
abipkgdiff *can* be large.  Rather, the patch manually waits for the
the spawned abipkgdiff to finish, and then, read its output.

	* tools/fedabipkgdiff (abipkgidff): Do not use Popen.communicate()
	as it might hang if the data is large.  Rather, busy wait for the
	abipkgdiff process to finish and then get its output.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>

tools/fedabipkgdiff

@@ -1021,7 +1021,25 @@ def abipkgdiff(cmp_half1, cmp_half2):
 
     proc = subprocess.Popen(' '.join(cmd), shell=True,
                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    stdout, stderr = proc.communicate()
+    # So we could have done: stdout, stderr = proc.communicate()
+    # But then the documentatin of proc.communicate says:
+    #
+    #    Note: The data read is buffered in memory, so do not use this
+    #    method if the data size is large or unlimited. "
+    #
+    # In practice, we are seeing random cases where this
+    # proc.communicate() function does *NOT* terminate and seems to be
+    # in a deadlock state.  So we are avoiding it altogether.  We are
+    # then busy looping, waiting for the spawn process to finish, and
+    # then we get its output.
+    #
+
+    while True:
+        if proc.poll() != None:
+            break
+
+    stdout = ''.join(proc.stdout.readlines())
+    stderr = ''.join(proc.stderr.readlines())
 
     is_ok = proc.returncode == ABIDIFF_OK
     is_internal_error = proc.returncode & ABIDIFF_ERROR or proc.returncode & ABIDIFF_USAGE_ERROR