Using userDataDir causes bug in opening scenarios.

I run 3 scenarios in my `allMyBackStopTests.js` file. If I run `backstop reference` with `debugWindow: true` I see 3 Chrome instances run and the correct 3 screenshots are taken.

This is the console output for the `reference`:

COMMAND | Executing core for `reference`
clean | backstop_data/bitmaps_reference was cleaned.
createBitmaps | Selected 3 of 3 scenarios.
searching for 3 available ports.
These ports will be used: [9222,9223,9224]
Starting Chromy: {"chromeFlags":["--disable-gpu","--force-device-scale-factor=1","--disable-infobars=true","--window-size=1024,768"],"port":9222,"waitTimeout":30000,"visible":true}
CREATING NEW REFERENCE FILES
Cookie state restored with: []
SCENARIO > Tweakers
Starting Chromy: {"chromeFlags":["--disable-gpu","--force-device-scale-factor=1","--disable-infobars=true","--window-size=1024,768"],"port":9223,"waitTimeout":30000,"visible":true}
CREATING NEW REFERENCE FILES
Cookie state restored with: []
SCENARIO > Groningen
Starting Chromy: {"chromeFlags":["--disable-gpu","--force-device-scale-factor=1","--disable-infobars=true","--window-size=1024,768"],"port":9224,"waitTimeout":30000,"visible":true}
CREATING NEW REFERENCE FILES
Cookie state restored with: []
SCENARIO > Umbrella
9223 Chrome v64 detected.
9222 Chrome v64 detected.
9224 Chrome v64 detected.
9222 INFO > BackstopTools have been installed.
9224 LOG > ReferenceError: tagging is not defined
9224 LOG > ReferenceError: tagging is not defined
9224 INFO > You are running Vue in development mode.
Make sure to turn on production mode when deploying for production.
See more tips at https://vuejs.org/guide/deployment.html
9224 INFO > BackstopTools have been installed.
9223 INFO > BackstopTools have been installed.

For my project I would like to add my Chrome history/cache/cookies, so I add:

"engineOptions": {
"userDataDir": "C:/Users/Peter/AppData/Local/Google/Chrome/User Data/Default"
}

When I run `backstop reference` now I get one Chrome instance with 3 tabs but only one tab (the last) will open the needed URL and only 1 screenshot is taken for the reference.

This is the log for the `reference` with `userDataDir` enabled:

COMMAND | Executing core for `reference`
clean | backstop_data/bitmaps_reference was cleaned.
createBitmaps | Selected 3 of 3 scenarios.
searching for 3 available ports.
These ports will be used: [9222,9223,9224]
Starting Chromy: {"chromeFlags":["--disable-gpu","--force-device-scale-factor=1","--disable-infobars=true","--window-size=1024,768"],"port":9222,"waitTimeout":30000,"visible":true,"userDataDir":"C:/Users/Peter/AppData/Local/Google/Chrome/User Data/Default"}
CREATING NEW REFERENCE FILES
Cookie state restored with: []
SCENARIO > Tweakers
Starting Chromy: {"chromeFlags":["--disable-gpu","--force-device-scale-factor=1","--disable-infobars=true","--window-size=1024,768"],"port":9223,"waitTimeout":30000,"visible":true,"userDataDir":"C:/Users/Peter/AppData/Local/Google/Chrome/User Data/Default"}
CREATING NEW REFERENCE FILES
Cookie state restored with: []
SCENARIO > Groningen
Starting Chromy: {"chromeFlags":["--disable-gpu","--force-device-scale-factor=1","--disable-infobars=true","--window-size=1024,768"],"port":9224,"waitTimeout":30000,"visible":true,"userDataDir":"C:/Users/Peter/AppData/Local/Google/Chrome/User Data/Default"}
CREATING NEW REFERENCE FILES
Cookie state restored with: []
SCENARIO > Umbrella
9223 Chrome v64 detected.
9223 INFO > BackstopTools have been installed.