Catch OSError instead of PermissionError when making log dir

[CasperWA]

Fixes #448

[codecov]

Codecov Report

Merging #449 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #449   +/-   ##
=======================================
  Coverage   91.60%   91.60%           
=======================================
  Files          60       60           
  Lines        2800     2800           
=======================================
  Hits         2565     2565           
  Misses        235      235           

Flag	Coverage Δ
#unittests	91.60% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
optimade/server/logger.py	76.66% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 033800d...91efeba. Read the comment docs.