Osrm datastore stability

[ctudorache]

Issue

Osrm-datastore stability fixes:

• test if old shm segment exists before swapping data
• on signal handler (SIGTERM, SIGABRT, ..): -- avoid deleting the global shared object "osrm-region" -- release the global mutex

Tasklist

• [ ] CHANGELOG.md entry (How to write a changelog entry)
• [ ] update relevant Wiki pages
• [ ] add tests (see testing documentation
• [ ] review
• [ ] adjust for comments
• [ ] cherry pick to release branch

Requirements / Relations

Link any requirements here. Other pull requests this PR is based on?