Test Metrics: Add test case to write and read a 100MB file in /data

[lifeeth]

This test case would allow us to see trends over time of I/O speeds. Since Robot framework automatically records the execution time of test cases - we could just have two cases one just writing from /dev/null to a 100MB file and one reading from the 100 MB file to /dev/null using dd.

1. Helps us in predicting a failure of the hardware rig.
2. Find regressions in kernel configurations causing SDcard I/O slow downs.
3. Allow us to have a rig to benchmark different SD card speeds.