Tramp code cleanup

* lisp/net/tramp-sh.el (tramp-find-shell, tramp-find-inline-compress)
(tramp-get-remote-path):
* lisp/net/tramp-smb.el (tramp-smb-handle-process-file):
Use `tramp-warning'.

* test/lisp/net/tramp-tests.el (tramp--test-container-p):
Add "kubernetes", "run0" and "nspawn".
(tramp--test-toolbox-p): New defun.
(tramp-test45-asynchronous-requests): Use it.
(tramp--test-check-files): Adapt regexp.

lisp/net/tramp-sh.el

@@ -4468,8 +4468,8 @@ file exists and nonzero exit status otherwise."
 			;; Maybe it works at least for some other commands.
 			(prog1
 			    default-shell
-			  (tramp-message
-			   vec 2
+			  (tramp-warning
+			   vec
 			   (concat
 			    "Couldn't find a remote shell which groks tilde "
 			    "expansion, using `%s'")
@@ -5003,8 +5003,8 @@ Goes through the list `tramp-inline-compress-commands'."
 
 	(tramp-set-connection-property p "inline-compress" nil)
 	(tramp-set-connection-property p "inline-decompress" nil)
-	(tramp-message
-	 vec 2 "Couldn't find an inline transfer compress command")))))
+	(tramp-warning
+	 vec "Couldn't find an inline transfer compress command")))))
 
 (defun tramp-ssh-option-exists-p (vec option)
   "Check, whether local ssh OPTION is applicable."
@@ -5714,8 +5714,8 @@ Nonexistent directories are removed from spec."
 		   (tramp-shell-quote-argument tramp-end-of-heredoc))
 		  'noerror (rx (literal tramp-end-of-heredoc)))
 		 (progn
-		   (tramp-message
-		    vec 2 "Could not retrieve `tramp-own-remote-path'")
+		   (tramp-warning
+		    vec "Could not retrieve `tramp-own-remote-path'")
 		   nil)))))
 
 	;; Replace place holder `tramp-default-remote-path'.

lisp/net/tramp-smb.el

@@ -1231,7 +1231,7 @@ PRESERVE-UID-GID and PRESERVE-EXTENDED-ATTRIBUTES are completely ignored."
 	 ((car destination)
 	  (setq outbuf (current-buffer))))
 	;; stderr.
-	(tramp-message v 2 "%s" "STDERR not supported"))
+	(tramp-warning v "%s" "STDERR not supported"))
        ;; 't
        (destination
 	(setq outbuf (current-buffer))))

lisp/net/tramp.el

@@ -4862,10 +4862,11 @@ should be set conmnection-local.")
     (when (and (not (tramp-compat-connection-local-p
 		     tramp-direct-async-process))
 	       (tramp-connection-property-p v "direct-async-process"))
-      (let ((msg (concat "Connection property \"direct-async-process\" is deprecated, "
-			 "use connection-local variable `tramp-direct-async-process'\n"
-			 "See (info \"(tramp) Improving performance of "
-			 "asynchronous remote processes\")")))
+      (let ((msg (concat
+		  "Connection property \"direct-async-process\" is deprecated, "
+		  "use connection-local variable `tramp-direct-async-process'\n"
+		  "See (info \"(tramp) Improving performance of "
+		  "asynchronous remote processes\")")))
 	(if (tramp-get-connection-property
 	     tramp-null-hop "direct-async-process-warned")
 	    (tramp-message v 2 msg)