Upgrade to Terraform v0.10

[austinbyers]

Upgrades to Terraform v0.10! This lets us upgrade to the latest AWS provider and supports interactive approval during each apply operation.

No work is required for users to upgrade as long as the latest terraform binary is in their PATH.

During a deploy, the user is now required to explicitly approve the changes for the main apply. However, the second apply (which only updates Lambda aliases) happens automatically, because it shouldn't even be necessary. If the Lambda function updates (and the user approves), then its alias will have to update as well. It would also be annoying for the user to have to explicitly approve twice on every deploy.

Resolves: #32 (Terraform v0.10)
Required for: #6 (Cloudwatch dashboard)

Tested

Tested with a deploy and live_test. A deploy now looks like this:

$ python3 manage.py deploy
...
Do you want to apply these changes?
  Terraform will apply the changes described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes
...

Reviewers

to: @jacknagz
cc: @airbnb/binaryalert-maintainers

[coveralls]

Coverage remained the same at 86.508% when pulling fefa161 on abb--terraform-0-10-2 into 6134b33 on master.

[jacknagz]

do users have to run terraform init to get the new provider?

[austinbyers]

@jacknagz , yes terraform init is required to get the provider, but BinaryAlert runs that automatically on every deploy anyway

[jacknagz]

@austinbyers sounds good, just wanted to verify

[coveralls]

Coverage remained the same at 86.548% when pulling 6cb7d69 on abb--terraform-0-10-2 into 2ef588b on master.