Fix playback with build scripts

[celinval]

Description of changes:

I'm not 100% sure on why we need to set target, but without it, cargo is not properly running the build scripts as part of playback subcommand. I added that + made sure we propagate RUSTFLAGS to playback as well.

Resolved issues:

N/A

Related RFC:

Optional #ISSUE-NUMBER.

Call-outs:

Adding --target also caused compilation for our tests to generate an extra artifact. Thus, I had to change an existing test.

Testing:

• How is this change tested? New test

• Is this a refactor change?

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[jaisnan]

Lgtm!