Disable curl progress bar when running vagrant up

Removes this ugly output, but preserves the error messages.

```
    master: Running: inline script
==> master:  
==> master:  
==> master: %
==> master:  
==> master: R
==> master: e
==> master: c
==> master: e
==> master: i
==> master: v
==> master: e
==> master: d
==> master:  
==> master: %
==> master:  
==> master: X
==> master: f
==> master: erd  Average Speed   Time    Time     Time  Current
==> master:                                  Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0

```