flux-mini: change default units of --time-limit to minutes

Problem: The -t, --time-limit=FSD option of flux-mini is in FSD,
which defaults to seconds when no units are explicitly supplied,
but traditional resource managers with similar options default to
minutes and this has been confusing first-time users.

Change the interpretation of only the --time-limit option to default
to minutes when no units are supplied.

Fixes #4552

Author: grondo

src/cmd/flux-mini.py

@@ -461,8 +461,9 @@ def create_parser(exclude_io=False):
             "-t",
             "--time-limit",
             type=str,
-            metavar="FSD",
-            help="Time limit in Flux standard duration, e.g. 2d, 1.5h",
+            metavar="MIN|FSD",
+            help="Time limit in minutes when no units provided, otherwise "
+            + "in Flux standard duration, e.g. 30s, 2d, 1.5h",
         )
         parser.add_argument(
             "--urgency",
@@ -614,6 +615,13 @@ def jobspec_create(self, args):
                 list_split(args.requires),
             )
         if args.time_limit is not None:
+            #  With no units, time_limit is in minutes, but jobspec.duration
+            #  takes seconds or FSD by default, so convert here if necessary.
+            try:
+                limit = float(args.time_limit)
+                args.time_limit = limit * 60
+            except ValueError:
+                pass
             jobspec.duration = args.time_limit
 
         if args.job_name is not None: