builder/amazon/ebs: Add config for target AZ.

Fixes [GH-536]
builder/amazon/common: Add AvailZone to StepRunSourceInstance struct

[GH-536]
Fixes missing entropy in the uuid package.

math/crypto is seeded with 1 and thus will create predictable UUIDs. Because
amazon-instance and amazon-ebs in the same second when building both targets
the timestamp in front doesn't help either. See #552
Arguments Prefix (--) was missing for (data)portconfig
Simplifies the implementation of common/uuid
Merge pull request #557 from zimbatm/unique-uuids

Fixes missing entropy in the uuid package.
Update CHANGELOG
Merge branch 'master' of github.com:mitchellh/packer into fix#536

Conflicts:
	CHANGELOG.md
packer: don't panic if can't write to UI
Merge pull request #558 from fabiang/virtualbox-sata

builder/virtualbox: arguments Prefix (--) was missing for (sata)portconfig
Merge pull request #550 from mitchellh/fix#536

builder/amazon/ebs: Add config for target AZ.
builder/amazon: rename availzone to availability zone
builder/amazon/instance: support AZ here too
website: remove extra period.
spelling mistake in comments
Added missing close-curly-brace to default value of execute_command.
Merge pull request #564 from mmercer-appneta/master

Added missing close-curly-brace to default value of execute_command in Chef Solo docs
Merge pull request #572 from ktruong7/format-issues1

Spelling mistake in comments
s/extremely to/extremely easy to/
Merge pull request #575 from ciarand/feature/fix-typo

Fix typo in documentation