Fix VirtualBox and Parallels executors registration bugs

What does this MR do?

Fix virtualbox executor registration bug.

Why was this MR needed?

Registration virtualbox executor runner by non-interactive, Don't write ssh settings.

$ gitlab-ci-multi-runner register \
  -u http://gitlab.example.com/ci \
  -r xxxxxx \
  --tag-list foo \
  --executor virtualbox \
  --ssh-user abc \
  --ssh-host foo.bar \
  --virtualbox-base-name vbox1 \
  -n

concurrent = 1
check_interval = 0

[[runners]]
  name = "vanp"
  url = "http://gitlab.example.com/ci"
  token = "d703f5b1acc01233de252cbd4fbe7f"
  executor = "virtualbox"
  [runners.cache]

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Tries to resolve #2120 (closed).