Drill 4313 - Improve method of picking a random drillbit from the C++ client

[parthchandra]

There are two changes here -

1. Set the seed for the random generator only at initialization time
2. Use a random shuffle on the list of drillbits and pick one after this. For a small sample of drillbits, this seems to give a more uniform selection of drillbits.

Also a protobuf class changed so some code had to be updated for that. Included as a separate commit in the PR

[amansinha100]

+1. LGTM.