KUDU-811: gflag style guide
KUDU-811: gflag style guide

This will be used for future gflags as well as for a massive overhaul of
existing ones.

Change-Id: I5b18bd3bbb223a64272ba37ef77b3f25f512fa65
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/7380
Tested-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@cloudera.com>

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