common/config: config filter function [GH-521]

Fixes #521
common/config: strip keys appropriate for OpenStack.
communicator/ssh: explicitly set c.conn = nil
Merge pull request #531 from mitchellh/521

common/config: config filter function [GH-521]
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Merge pull request #522 from patricklucas/fix_instance_not_found_race

builder/amzon: fix race condition after launching EC2 instance
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Merge pull request #512 from hoshposh/vbox-shutdown-issue

builder/virtualbox: sleep after shutdown before export to avoid session locks
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Merge pull request #503 from zimbatm/fix/vagrant-aws-instance

post-processor/vagrant: support instance store AMIs [GH-503]
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I found that I needed the shutdown command to be run as root.

Also added a note about shutdown_command that bit me.
provisioner/shell: fix EOF detection

Fixes #507

The scanUnixLine function was erroneously returning empty lines when EOF
was reached.
This commit adds a test for the problem and changes the scanUnixLine
function to elide the trailing \n if no content was read.
Merge pull request #537 from mitchellh/fix507

provisioner/shell: fix EOF detection
provisoiner/shell: append only needs to add a byte for UnixReader
provisioner/shell: comment on why we return right away if advance == 0

/cc @mwhooker
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Remove dependency on identifier package, use time ordered UUID [GH-541]
command/build: remove asserts framewor
builder/amazon,builder/openstack: remove more cgl libs