Arista SSH not closing connections correctly

[Gobam]

Description of Issue/Question

Napalm is not closing correctly the objects created for Arista SSH session. We identified this when noted a thread that remains open after a getter is completed for an EOS device. Trying to use the close() method is causing an exception (see below)

Did you follow the steps from https://github.com/napalm-automation/napalm#faq

• Yes
• [] No

Setup

napalm version

napalm==4.0.0

Network operating system version

vEOS
Hardware version: 
Serial number: 
Hardware MAC address: 5000.005b.6ff5
System MAC address: 5000.005b.6ff5

Software image version: 4.26.1F
Architecture: x86_64
Internal build version: 4.26.1F-22602519.4261F
Internal build ID: 1eca5f74-3ced-441a-9137-c966e8f0319d
Image format version: 01.00

Uptime: 0 weeks, 4 days, 8 hours and 42 minutes
Total memory: 2006832 kB
Free memory: 953144 kB

Steps to Reproduce the Issue

Run a script including a Napalm getter inside a loop and monitor the threads. It will show a new thread after each run:

import napalm
from threading import enumerate

eos = napalm.get_network_driver("eos")

optional_args={
    'port':22,
    'transport': 'ssh',
}

for _ in range(10):
    # Connect:
    device = eos(
        hostname="192.168.0.1",
        username="user",
        password="password",
        optional_args=optional_args
    )

    device.open()
    result = device.get_interfaces()
    #device.close()
    print(result)

    for thread in enumerate():
        print(thread.name)

device.close() is commented as it causes an exception

Error Traceback

Traceback (most recent call last):
  File "test_napalm.py", line 21, in <module>
    device.close()
  File ".../venv/lib/python3.8/site-packages/napalm/eos/eos.py", line 234, in close
    if hasattr(self.device.connection, "close") and callable(
AttributeError: 'AristaSSH' object has no attribute 'connection'