network: uniform network parameters

* Move networktests.sh and networkstress.sh parameters to network.sh.
  Both network scripts have the same settings (e.g. RHOST), and
  some of the stress test parameters can be used by other net-tests,
  such as LHOST_IFACES and RHOST_IFACES variables.
* Add network features group to networkstress.sh.
* Add network features group to 'whole' group.

New test_net.sh functions:
* 'tst_get_ifaces TYPE' get test interface names for local/remote host
  (Note that it returns already defined iface list);
* 'tst_get_hwaddrs TYPE' get addresses from defined test interface names;
* 'tst_hwaddr TYPE LINK' get test HW address;
* 'tst_iface  TYPE LINK' get test interface name;

TYPE can be 'rhost' or 'lhost' (default).
LINK is the test link number starting from 0 (default).

Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>