homed: generate proper error if we cannot create mountpoint for homedir

Let's make this easier to debug. (When this failed for me due to disk
full it took me a bit to figure out what was going on.)

(cherry picked from commit 5b759bf)
(cherry picked from commit 8158c87c36d5725818a2a9cda4270b8839553f86)
(cherry picked from commit 6d33cf046a2064dd11ca9a1ee6d8f2d2356f4f10)
(cherry picked from commit 756d41d)
(cherry picked from commit 8e901fe)

Author: poettering

src/home/homework-mount.c

@@ -142,7 +142,9 @@ int home_move_mount(const char *mount_suffix, const char *target) {
         } else
                 d = HOME_RUNTIME_WORK_DIR;
 
-        (void) mkdir_p(target, 0700);
+        r = mkdir_p(target, 0700);
+        if (r < 0)
+                return log_error_errno(r, "Failed to create directory '%s': %m", target);
 
         r = mount_nofollow_verbose(LOG_ERR, d, target, NULL, MS_BIND, NULL);
         if (r < 0)