Further clarify 'too many values to unpack' error.

Many errors in yaml configurations cause ValueError to get thrown
with the message 'too many values to unpack.'  A previously reverted
change tried to handle all these situations and print an appropriate
message.

The current behavior of throwing the ValueError exception and exiting
is probably what we still want in these cases.  So instead of handling
the error, the code now checks for the exception at the top-most call
and displays appropriate messages in log.error and in the ctx.summary
data itself.

Fixes: 7510
Signed-off-by: Warren Usui <warren.usui@inktank.com>

teuthology/run_tasks.py

@@ -82,6 +82,15 @@ def run_tasks(tasks, ctx):
             from .task import interactive
             log.warning('Saw failure, going into interactive mode...')
             interactive.task(ctx=ctx, config=None)
+        # Throughout teuthology, (x,) = y has been used to assign values
+        # from yaml files where only one entry of type y is correct.  This
+        # causes failures with 'too many values to unpack.'  We want to
+        # fail as before, but with easier to understand error indicators.
+        if type(e) == ValueError:
+            if e.message == 'too many values to unpack':
+                emsg = 'Possible configuration error in yaml file'
+                log.error(emsg)
+                ctx.summary['failure_info'] = emsg
     finally:
         try:
             exc_info = sys.exc_info()