Incorrect volume location used when creating bootable installers from legacy versions on Apple Silicon

[sulliops]

@ninxsoft I believe this broke bootableinstaller.

I think it's supposed to be:

        arguments += ["--volume", volume, "--nointeraction"]

Originally posted by @jasisk in #166

---

The use of the incorrect volume URL when creating bootable installers from legacy versions on Apple Silicon hosts prevents the bootable installers from being created.

For example, using mist download mist download installer "10.12.6" bootableinstaller --bootable-installer-volume /path/to/volume:

┌───────────────────────────┐
│ BOOTABLE INSTALLER VOLUME │
└───────────────────────────┘
  ├─ Copying '/Volumes/10.12.6-16G29/Applications/Install macOS Sierra.app' to '/var/folders/zz/zyxvpxvq6csfxvn_n0000000000000/T/Install macOS Sierra.ad-hoc-code-signatures.app'...
  ├─ Ad-hoc code signing '/var/folders/zz/zyxvpxvq6csfxvn_n0000000000000/T/Install macOS Sierra.ad-hoc-code-signatures.app'...
  ├─ Creating bootable macOS Installer at mount point '/Volumes/Install OS X Yosemite'...
  └─ Invalid Exit Status Code: '254', Message: /Volumes/Install macOS Sierra is not a valid volume mount point.