Userland+SystemMonitor: Recognize the MS_RDONLY mount flag

Author: https://github.com/bugaevc
Commit: 4b300e085d
Pull-request: https://github.com/SerenityOS/serenity/pull/2430
Reviewed-by: https://github.com/alimpfard

Userland/chroot.cpp

@@ -57,6 +57,8 @@ int main(int argc, char** argv)
                     flags |= MS_NOEXEC;
                 else if (part == "nosuid")
                     flags |= MS_NOSUID;
+                else if (part == "ro")
+                    flags |= MS_RDONLY;
                 else if (part == "bind")
                     fprintf(stderr, "Ignoring -o bind, as it doesn't make sense for chroot\n");
                 else