Add a fixed length string Parquet benchmark

[bmcdonald3]

Add a Parquet string read benchmark that compares the performance of reading Parquet files with a fixed number of characters with and without the fixed length optimization. This will test (1) single file reads (2) multi-file reads with larger files (3) multi-file reads with smaller files and (4) all of the previous with the fixed length optimization.

Here are results demonstrating ~2x speedup with using the fixed length string optimization collected on a Cray XC with a Lustre file system:

test	sec
single-file	39.388
fixed-single	20.664
scaled-five	17.283
fixed-scaled-five	8.814
five	85.332
fixed-five	43.743
scaled-ten	8.998
fixed-scaled-ten	4.794
ten	86.761
fixed-ten	45.498