TMP directory for Apache poi can be read-only (Issue 293)

[janblom]

The proposed solution is to only use an alternative strategy for the tmp dir for Apache poi if the readonly situation situation. If not, proceed as before. A property org.ohdsi.whiterabbit.poi.tmpdircan be optionally used to control the location where the tmp dir is created.

Solves issue 293

[blootsvoets]

Looks fine to me. Just to clarify, the only way to be sure that you can write to a directory is to actually write a file to it. Unfortunately, Files.isWritable is not enough because it doesn't test all additional directory annotations that may exist.
It would be good to add a README / Wiki line about this new property.

FYI, on windows, changing the TMP environment value also changes the base temp directory. On all systems, java -Djava.io.tmpdir=/path/to/tmpdir changes the base temp directory.