Fixed remove_on_fail implementation

We need to clone session to be sure that the session will be used only
in one transaction simultaneously
addr: new thread-safe helpers to print address strings
addr: use getnameinfo() to properly determine family and automatically dereference sockaddr
session: get rid of handmade address-to-string conversion, use dnet_addr_string() and friends helpers
core: reset state if dnet_idc_update_backend has been failed.
Merge pull request #555 from iderikon/master

Fixed remove_on_fail implementation
v2.26.3.31
pytests: made server node isolated - now server nodes do not know about each other.
pytests: added test case for checking correct handling situation when 2 backends from different nodes has equal group and ids.
tests: created config struct for create_nodes method and moved all argument to it.
Merge pull request #557 from shaitan/master

Reset state if dnet_idc_update_backend has been failed.
v2.26.3.32
pytests: fixed broken index tests - use common cluster for all test and isolated cluster for test_special_cases.
Merge pull request #559 from shaitan/master

pytests: fixed broken index tests - use common cluster for all test and ...
speed up dc recovery as don't spend time on pickling/unpickling data and concatenate files via cat.
Change file concatenation from calling cat to python file read+write
use shutil.copyfileobj to concatinate files
lookup: extended lookup address to return dnet_addr, not address string
v2.26.3.33
Merge branch 'master' of https://github.com/reverbrain/elliptics into dc-recovery-fix-on-cat