Ignoring SSHKeyBadOwner if user is root (uid 0)

Allows using `sudo vagrant up` without `chown`ing the insecure private key
Scrub SSH PTY output to filter out command echo-ing.
Use -f argument to rm to force-remove files.

When using pty=true, removing files using sudo may request confirmation,
which will hang the connection.

Similarly, sometimes assumptions about file existence may be wrong and
in those cases it seems better to continue on as long as the file does
not exist, so -f makes sense there, too.
Preserve exit code while using pseudo-terminal hack.
Merge pull request #4410 from lsimons/use-rm-with-f

Use -f argument to rm to force-remove files.
Update CHANGELOG
core: better bundler errors
guests/linux: more verbose output when shared folder mount fails
[GH-4403]
commands/provision: don't advertise parallel [GH-4398]
Merge pull request #4408 from lsimons/ssh-scrub-pty-output-for-upstream

core: Scrub SSH PTY output to filter out command echo-ing and most other cruft
communicators/ssh: cleanup PTY code for GH-4408]
guests/linux: backoff a bit on the mount timeout [GH-4403]
Merge pull request #4387 from BackSlasher/allow-sudo

Ignoring SSHKeyBadOwner if user is root (uid 0)