Bug Report: Scan proceeds if "--filename" argument is not writeable

[bdorney]

Brief summary of issue

If the user supplies a --filename argument that is not writeable the scan writes a standard ROOT error message to the terminal however it continues to run.

This can contribute to data loss and lost time since the data taken will never be written to disk.

Most likely this issue impacts all our scan scripts.

Types of issue

• Bug report (report an issue with the code)
• Feature request (request for change which adds functionality)

Expected Behavior

If the --filename argument is not writeable the scan should exit instead of continuing.

Current Behavior

The scan proceeds. See for example: http://cmsonline.cern.ch/cms-elog/1026403

Steps to Reproduce (for bugs)

1. Run a python scan with a non-writeable filepath

Context (for feature requests)

Prevent data loss during longer measurements.

Your Environment

• Version used: dc39a28
• Shell used: zsh