Exec mixin requires called executable to be on the path or specified with a relative path

[carolynvs]

Describe the bug

When I rebuilt the otel-jaeger example with porter v1.0.1, I noticed that it broke the bundle. Previously the bundle was running the helpers script with helpers.sh without a relative path prefix. That worked when it was built with porter v1.0.0-alpha.20. Something we did since then broke calling the script that way, and it now gives an error about helpers.sh not being on the path.

To Reproduce

1. Checkout the example bundles repository
2. cd to otel-jaeger
3. porter build && porter install --allow-docker-host-access

Expected behavior

The bundle should install successfully but instead it fails.

Porter Command and Output

$ porter install --allow-docker-host-access
TRUNCATED
/cnab/app helpers.sh set-config
couldn't run command /cnab/app helpers.sh set-config: exec: "helpers.sh": executable file not found in $PATH
Error: couldn't run command /cnab/app helpers.sh set-config: exec: "helpers.sh": executable file not found in $PATH
exit status 1

Version

1.0.1

[schristoff]

This issue is linked here too with recreation steps.
Basically, before the exec mixin could be ran like this:

- exec:
      description: "Create OpenTelemetry configuration"
      command: helpers.sh
      arguments:
        - set-config
  - docker-compose:

But now it needs to be:

- exec:
      description: "Create OpenTelemetry configuration"
      command: ./helpers.sh
      arguments:
        - set-config
  - docker-compose:

or else we get the error pasted above. One thing when we go to support this is that it still works for all OSes