Threads for block stream does not close after connection close.

[stepanLav]

Version
Branch: support/1.2.x
Found on image hyperledger/iroha:latest by iroha-python library user.

Detail description:
After closing a connection for block stream the thread created for this connection is not closed.

Script for reproducing:
block_getter.py.zip

Actual result:
Memory consumption increases with each connection created.
log file:
iroha.log

[shazz]

@stepanLav, in addition to this bug, I noticed that each time that a transaction is performed thru the python client, the iroha memory increases but never goes down. Is it expected?

View of my 3 nodes (the python client only communicates with the red one), 2 days.