This commit ensures that the series file should work appropriately on
32-bit architecturs. It does this by reducing the maximum size of a
series file to 512MB on 32-bit systems, which should be fully
addressable.
It further updates tests so that the series file size can be reduced
further when running many tests in parallel on 32-bit architectures.
The DropSeries code path ended up creating a MeasurementSeriesIterator
for each dropped series, this was too expensive just to see if a
series exists.
This adds a HasSeries func and fixes and issue where TSI files were
compacted while an iterator was still in use causing a panic.