flux-mini: do not allow option abbreviation

Problem: flux-mini currently accepts option abbreviations since this
is default argparse behviour. However, this means `flux mini run` accepts
`--cores=N` for `--cores-per-task`, which could confuse users.

Set the allow_abbrev=False flag on flux-mini ArgumentParser() constructor.

Author: grondo

src/cmd/flux-mini.py

@@ -452,7 +452,7 @@ def create_parser(exclude_io=False):
         """
         Create default parser with args for mini subcommands
         """
-        parser = argparse.ArgumentParser(add_help=False)
+        parser = argparse.ArgumentParser(add_help=False, allow_abbrev=False)
         parser.add_argument(
             "-t",
             "--time-limit",