about the cache to be re-enable for example
```
DEBUG:urllib3.connectionpool:https://netbox.local:443 "GET /api/dcim/inventory-items/?device_id=9&tag=hw-disk&limit=0 HTTP/1.1" 200 52
('A cache backup failure has occurred. Please execute the "reenablecache" '
'command')
Traceback (most recent call last):
File "/usr/bin/netbox_agent", line 33, in <module>
sys.exit(load_entry_point('netbox-agent==0.7.1', 'console_scripts', 'netbox_agent')())
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/cli.py", line 50, in main
return run(config)
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/cli.py", line 43, in run
server.netbox_create_or_update(config)
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/server.py", line 417, in netbox_create_or_update
self.inventory.create_or_update()
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/inventory.py", line 547, in create_or_update
self.do_netbox_disks()
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/inventory.py", line 417, in do_netbox_disks
disks = self.get_hw_disks()
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/inventory.py", line 332, in get_hw_disks
for raid_card in self.get_raid_cards(filter_cards=True):
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/inventory.py", line 242, in get_raid_cards
self.raid = raid_class()
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/raid/hp.py", line 180, in __init__
self.convert_to_dict()
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/raid/hp.py", line 185, in convert_to_dict
controllers = _parse_ctrl_output(lines)
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/raid/hp.py", line 34, in _parse_ctrl_output
attr, val = line.split(': ', 1)
```
```
Traceback (most recent call last):
File "/usr/bin/netbox_agent", line 33, in <module>
sys.exit(load_entry_point('netbox-agent==0.7.1', 'console_scripts', 'netbox_agent')())
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/cli.py", line 50, in main
return run(config)
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/cli.py", line 43, in run
server.netbox_create_or_update(config)
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/server.py", line 417, in netbox_create_or_update
self.inventory.create_or_update()
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/inventory.py", line 550, in create_or_update
self.do_netbox_disks()
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/inventory.py", line 420, in do_netbox_disks
disks = self.get_hw_disks()
File "/opt/netbox-agent/lib/python3.6/site-packages/netbox_agent/inventory.py", line 344, in get_hw_disks
size = int(disk.get('size', 0))
TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'
```
The function parsing the RAID logical volumes in the HP module did not
manage the case where disks were set in JBOD mode, thus having no RAID
array set.
This patch fixes this by checking if arrays are defined on pdisks before
parsing the logical disks.
Also added returncode read when executing the RAID related commands to
raise a more precise error.
