[containerization] Ensure volume mounts are unique directories with trailing slash

[cidrblock]

Fixes #727
Fixes ansible/ansible-navigator#471

• Clear up logic, ensure src and dest are always directories with a trailing slash
• Ensure abs, expand user and vars for each
• Remove unused func for trailing slash adding as it is within the only func using it
• Add sufficient unit test to cover all scenarios
• 1 var rename for consistency with src
• Fix safe path mount to cover with and without trailing slash
• change log file to unique to avoid suspected race condition

[cidrblock]

recheck

[cidrblock]

recheck