remote: manually close all ssh pools at the end

Python 2 fails to do it automatically occasionally and shows weird error
messages.

This was harmless but confusing.

dvc/main.py

@@ -8,6 +8,7 @@ from dvc.cli import parse_args
 from dvc.config import ConfigError
 from dvc.analytics import Analytics
 from dvc.exceptions import NotDvcRepoError, DvcParserError
+from dvc.remote.ssh.pool import close_ssh_pools
 
 
 logger = logging.getLogger("dvc")
@@ -53,6 +54,9 @@ def main(argv=None):
         ret = 255
     finally:
         logger.setLevel(outerLogLevel)
+        # Python 2 fails to close these clean occasionally and users see
+        # weird error messages, so we do it manually
+        close_ssh_pools()
 
     Analytics().send_cmd(cmd, args, ret)
 

dvc/remote/ssh/pool.py

@@ -22,6 +22,12 @@ def get_ssh_pool(*conn_args, **conn_kwargs):
     return SSHPool(conn_args, conn_kwargs)
 
 
+def close_ssh_pools():
+    for pool in get_ssh_pool.memory.values():
+        pool.close()
+    get_ssh_pool.memory.clear()
+
+
 class SSHPool(object):
     def __init__(self, conn_args, conn_kwargs):
         self._conn_args = conn_args