build_daemon returns Version skew in a race condition

[grouma]

If two instances of the build daemon are started around the same time, only one will get a hold of the lock file. It should write a version file immediately after this. However, the second instance can try to read this version file before it is written, which will cause it to return a Version Skew. We can fix this by introducing a retry on the Version File if the value is null.

[grouma]

Alternatively we can write the version file inside the tryGetLock method instead of inside the daemon.start method which is called an indeterminable while after the lock is grabbed.