CLI support for extra user supplied terraform files

[ryandeivert]

to: @airbnb/streamalert-maintainers

Background

Users may have additional resources they'd like to create in terraform and track in the streamalert deployment state. We should support this concept.

Changes

• adding cli arg (--terraform-file) to supply additional terraform config files. the flag can be used multiple times to supply more than one file (similar to the terraform --target=... --target=.... logic)
• removing old tf cleanup code since temp path will be used for terraform configuration
  • Since runs should now be idempotent, a new temp file will be used every time the CLI is invoked
• adding cliconfig support for temp tf directory
• updates to tf_runner and run_command for temp tf path
• packaging change for tf temp path
• adding logic for copying files to tf temp path
• adding terraform_files section to general in config
• removing init backend option for CLI since backend init will have to happen every time the CLI is invoked now
  • [ ] TODO: decide if there is a better way for this since it could get annoying/slow?

Testing

Updates to various unit tests

[blakemotl]

Since the paths are supplied via command line arguments won't the user have to include them every time they deploy/build?

[ryandeivert]

@blakemotl good call, added a config option that gets merged with ones provided as cli args