Pytests and fixes

Pytests: used dnet_run_servers at instead of running dnet_ioserv and using cocaine-tools. Decreased default value for io_thread_num, nonblocking_thread_num, net_thread_num.
SRW: removed ability to specify nodes as dict at srw config.
Fixed memory corruption at histogram.
Removed specifying nodes as dict in srw config.
SRW tests in Pytests is still disabled because of crashes - continue investigating.