cache purging - non admin/root for read benchmark

[jamesmarkchan]

The typical read benchmark currently is easiest to perform when we do a write , drop cache and read test. the dropping of the cache requires elevated privileges. a technique other tools use is to write an amount of data larger than the systems' memory to flush the disk cache and then read data not in the cache to measure the read disk performance from that.

This mode which could be the new default would free our need to have the user run in administrator mode to drop the disk cache for the read benchmark.

the pollution purge operation:

1. get the size of system memory
2. create a single file that is x1.1 of system memory
3. delete the created file

this would replace the existing disk cache drop which requires admin and would be used if the program is not run in admin mode

Objectives:

• implement a mode where the cache is flushed when not run as administrator
• add time measurement to assess how long the flush operation is, log
• indicate to the user and update progress bar accordingly to account for flushing
• This mode should be used when the tool is not run as administrator or root
• if flush time does not affect user experience it could be the default mode

have @jslcom or @jamesmarkchan review implementation

[jamesmarkchan]

For describing to the user can also call it the "Buffer Overflow" method. Looks like good progress in that last pull request.