cli: in dry-run send the list of hosts to stdout

* To simplify the usage from additional tools of the generated list of
  hosts when not executing commands (dry-run mode), send the list to
  stdout while the rest of the output is sent to stderr.
* In conjunction with the -n/--no-color output it should allow for an
  easy piping into additional tools using:

  cumin -n QUERY 2> /dev/null

Bug: T212783
Change-Id: I689fd8a5d639571deda958d403d27a997752e691

cumin/cli.py

@@ -312,12 +312,15 @@ def get_hosts(args, config):
         return hosts
 
     stderr('{num} hosts will be targeted:'.format(num=len(hosts)))
-    stderr(Colored.cyan(cumin.nodeset_fromlist(hosts)))
+    # The list is sent to stdout or stderr based on the dry_run mode
 
     if args.dry_run:
+        tqdm.write(Colored.cyan(cumin.nodeset_fromlist(hosts)))
         stderr('DRY-RUN mode enabled, aborting')
         return []
 
+    stderr(Colored.cyan(cumin.nodeset_fromlist(hosts)))
+
     if args.force:
         stderr('FORCE mode enabled, continuing without confirmation')
         return hosts