[devtools] fix race when creating backupdir
If somebody else creates backupdir between our stat() and mkdir() (like,
say, another test running in parallel), we shouldn't crash.
/* * cubicweb js mock for unit tests * This module defines variables and functions used in quite a few places * in cw js framework that can't be used or guessed without a real CW server */varpageid='my-page-id';function_(message){returnmessage;}