flux-jobs: force default stdout encoding to utf-8

Problem: Python3 doesn't work well in non UTF-8 clean locales
such as C/POSIX. This will be especially true when RFC19 F58
encoded JOBIDs are supported in flux-jobs.

Force stdout to UTF-8 encoding in flux-jobs. This is only necessary
in python 3.6 since UTF-8 seems to be the default in 3.7 and
above.

src/cmd/flux-jobs.py

@@ -629,6 +629,9 @@ def color_reset(color_set):
 
 @flux.util.CLIMain(LOGGER)
 def main():
+
+    sys.stdout = open(sys.stdout.fileno(), "w", encoding="utf8")
+
     args = parse_args()
 
     if args.jobids and args.filtered: