"option to prevent guard,exit,hsdir flag assignment"

"A node will never receive the corresponding flag unless
that node is specified in the
TestingDirAuthVote{Exit,Guard,HSDir} list, regardless of
its uptime, bandwidth, exit policy, or DirPort".

Patch modified by "teor": VoteOnHidServDirectoriesV2
is now obsolete, so TestingDirAuthVoteHSDir always
votes on HSDirs.

Closes ticket 14882. Patch by "robgjansen".
Commit message and changes file by "teor"
with quotes from "robgjansen".