probe: Extend lizardfs-probe functionality

This commit reorganises lizardfs-probe to ease adding new commands and adds
following ones:
 * info: general information about the installation;
 * list-chunkservers: information about chunkservers;
 * list-disks: information about physical disks;
 * list-mounts: information about mountpoints.
Functional tests are also included.

Together with them, following changes in other parts of project are performed:
 * LizardFS constants can be passed to tests;
 * human_readable_format.* is extended and moved to 'common' subproject;
 * HDD and whole installation statistics mechanisms are rewritten to make use
   of C++ and serialization;
 * network tools are extended by polling function.

Change-Id: I6566b99030d50b11300d604476ac4677c9b518d2