providers/virtualbox: don't error when intnet set to "true" [GH-2751]
update changelog
Replace `exit 1` with `abort`

According to the documentation, Kernel.abort calls Kernel.exit(false). The failure status 1 is an implementation detail on Unix-like systems. In theory, a future system could exist where 1 indicates a successful exit and 0 indicates a failure.
Merge pull request #2752 from sferik/patch-1

core: replace `exit 1` with `abort`
core: accept passwords in ssh_info
communicators/ssh: support passwords
core: warn if password only on `vagrant ssh`
core: raise exceptions if they happen in WaitForCommunicator threads
insert_public_key cap, and use that if it exists
core: fix potential exception case in SSHExec middleware
communicators/ssh: output UI when inserting key
core: error if vagrant ssh -c with password
communicators/ssh: if insert_key is false, don't insert a key
website/docs: update docs for insert_key
Merge pull request #2754 from mitchellh/f-insert-private-key

Support password-based SSH, automatically insert insecure key
update CHANGELOG