Currently file provisioners will silently fail when there is an error
with the remote side. This commit checks the scp error code and will
return the error message from the remote.

builder/vmware: fix Fusion DhcpLeasesPath

Now the VMware builder should automatically pick between Fusion 5 and
Workstation 9, based on which one is installed.

This unifies all the builders so that they all wait for SSH using a common
step available in builder/common. This common step has the best practices of
every previously unique step, such as retrying SSH handshakes, limiting
the number of SSH handshakes, timeouts, and so on.

packer: Delete "override" key for config passed to provisioners

The overrides are processed, so that the provisioner only sees the
appropriate sub-settings, so the provisioner does not need the raw
overrides.

If we leave the top-level overrides object in the provisioner
configuration, then it will be rejected as an unknown configuration
key.