bind-add-zone: add bind zones using pdns_control

Add pdns_control for loading new zones without reloading named.conf.
Zone is added but not loaded, you should do it manually, by querying
something. Beware of cache, it is better to purge it before.
bind-add-zone: Add stress-test for bind-add-zone

Uses dnsperf. See README for details.
bind-add-zone: fix for tests context
bind-add-zone: verbose error message
bind-add-zone: rename test, fix timeout
bind-add-zone: add docs
bind-add-zone: lock reworked. caller of createDomain have to take lock
bind-add-zone: protect file with s_state_lock
Merge pull request #954 from paboldin/bind-add-zone

BIND backend: Add zones on pdns_control