cannot connect to BT 4.0 devices on 20.04

[Scott Hu]

[Summary]
cannot connect to BT 4.0 devices by checkbox, but GUI can

[Steps to reproduce]
1. Run bluetooth4/HOGP-mouse or bluetooth4/HOGP-keyboard

[Expected result]
Can connect to BT 4.0 devices normally

[Actual result]
Error msg shown:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/checkbox_support/bt_helper.py", line 159, in _scan_timeout
    dbus.Interface(adapter, ADAPTER_IFACE).StopDiscovery()
  File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 72, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 141, in __call__
    return self._connection.call_blocking(self._named_service,
  File "/usr/lib/python3/dist-packages/dbus/connection.py", line 652, in call_blocking
    reply_message = self.send_message_with_reply_and_block(
dbus.exceptions.DBusException: org.bluez.Error.InProgress: Operation already in progress

[Failure rate]
SRV5-DVT1-C3: 10/10

[Additional information]
SKU: SRV5-DVT1-C3, SRV5-DVT1-C4
Manifest: canonical-oem-somerville-focal-amd64-20200502-85+fossa-bulbasaur+X21
system-manufacturer: Dell Inc.
system-product-name: Vostro 5301
bios-version: 0.1.12
CPU: Genuine Intel(R) CPU 0000 @ 2.30GHz (8x)
GPU: 0000:00:02.0 VGA compatible controller [0300]: Intel Corporation Device [8086:9a49]
kernel-version: 5.6.0-1008-oem

[Scott Hu (huntu207)]

Automatically attached

[Scott Hu (huntu207)]

Automatically attached

[Scott Hu (huntu207)]

Automatically attached

[Scott Hu (huntu207)]

Automatically attached

[Maksim Beliaev (beliaev-maksim)]

Bug was migrated to GitHub: https://github.com/canonical/checkbox/issues/112.
Bug is no more monitored here.