Improve handling of lock handling defaults

[smgallo]

Description

Improve handling of cases when no lock directory or lock file prefix are specified. Rather than using the current directory when a lock directory has not been provided, use the system temp directory. Default to a lock file prefix of "etlv2_" but allow specifying an empty string for no prefix. This eliminates the case where the code assumes that the current directory is the lock directory and "cleans" files that are not associated with a running process.

Motivation and Context

Tests performed

Yes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project as found in the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.