Add GLM RUnit benchmark based on randomly created frame, running 1 iteration.
Reports timing of GLM for different row/col counts.

Example result (horizontal: cols, vertical: rows):

> # Report timing results
> data
         10   100   1000
10000 0.139 1.139  3.360
1e+05 0.124 1.207 30.817
Merge branch 'master' of https://github.com/0xdata/h2o