fix: default variable assignment and `tar` command syntax

[mdqst]

TITLE

Description

I’ve corrected two issues in the script:

1. The syntax for setting the default value for the NODE_EXPORTER_DIR variable was wrong. The corrected version now properly uses :- for default assignment in Bash:

   NODE_EXPORTER_DIR="${NODE_EXPORTER_DIR:-"$BASE_DIR/.node_exporter"}"
   

   This ensures that if NODE_EXPORTER_DIR isn’t set, it defaults to $BASE_DIR/.node_exporter.

2. Fixed the incorrect order of flags in the tar command. The -z flag for gzip compression should follow -x and precede -v. The corrected command is:

   if tar -xvzf $FILE; then
   

Both changes ensure the script runs without errors in these areas.

Type of change

Please delete options that are not relevant.

• [x] Optimization

Checklist

• [ ] “Hotfix” to testnet, everything else to staging
• [ ] Linked to Github Issue
• [ ] This change depends on code or research by an external entity
  • [ ] Acknowledgements were updated to give credit
• [ ] Unit tests added
• [ ] This change requires new documentation.
  • [ ] Documentation has been added/updated.
• [ ] This change is an Optimization
  • [ ] Benchmarks added/run
• [ ] Has a known issue
  • Link to the open issue addressing it
• [ ] If your PR changes the Operator compatibility (Ex: Upgrade prover versions)
  • [ ] This PR adds compatibility for operator for both versions and do not change batcher/docs/examples
  • [ ] This PR updates batcher and docs/examples to the newer version. This requires the operator are already updated to be compatible