DS: get rid of identification of dserv instances by PID
In current DS implementation dserv instances are identified the PID of dservd instance that initially created them.
It's not very good idea because DS doesn't do its resources cleanup properly when dservd exits abnormally (by receiving SIGSEGV/SIGKILL for example). In this case we have no way to catch that situation in kernel space and release all used resources.
The fix of described problem probably requires to change dserv instances identification mechanism from PID based to dserv instance