ci: log failed command line, and try enabling stdout line buffering

.ci/ci_lib.py

@@ -57,8 +57,10 @@ def have_docker():
 
 # -----------------
 
-# Force stdout FD 1 to be a pipe, so tools like pip don't spam progress bars.
+# Force line buffering on stdout.
+sys.stdout = os.fdopen(1, 'w', 1)
 
+# Force stdout FD 1 to be a pipe, so tools like pip don't spam progress bars.
 if 'TRAVIS_HOME' in os.environ:
     proc = subprocess.Popen(
         args=['stdbuf', '-oL', 'cat'],
@@ -86,8 +88,13 @@ def _argv(s, *args):
 def run(s, *args, **kwargs):
     argv = ['/usr/bin/time', '--'] + _argv(s, *args)
     print('Running: %s' % (argv,))
+    try:
         ret = subprocess.check_call(argv, **kwargs)
         print('Finished running: %s' % (argv,))
+    except Exception:
+        print('Exception occurred while running: %s' % (argv,))
+        raise
+
     return ret