CloudStack builder can't find service/disk offerings of ROOT domain in a CloudStack domain setting

_This issue was originally opened by @hrak in https://github.com/hashicorp/packer/issues/4541 and has been migrated to this repository. The original issue description is below._

---
When using domains in CloudStack, any disk or service offering created in the ROOT domain is not available for use in Packer in any other domain than ROOT, because the API call for discovering disk & service offerings does not pass the 'listall=true' flag.

As a workaround i have now duplicated a service offering from the ROOT domain in my team domain, but it would be nice if packer sees the default offerings of the ROOT domain.

Packer output:
```
cloudstack output will be in this color.

==> cloudstack: Preparing config...
==> cloudstack: 1 error(s) occurred:
==> cloudstack:
==> cloudstack: * Error retrieving UUID of disk offering : No match found for Medium: &{Count:0 DiskOfferings:[]}
Build 'cloudstack' finished.

==> Builds finished. The artifacts of successful builds are:
```

```
☁ Apache CloudStack 🐵 cloudmonkey 5.3.2. Type help or ? to list commands.

Using management server profile: local

(local) 🐵 > list diskofferings
(local) 🐵 >
(local) 🐵 > list diskofferings listall=true
{
"count": 3,
"diskoffering": [
{
"created": "2015-12-04T15:19:59+0000",
"disksize": 5,
"displayoffering": true,
"displaytext": "Small Disk, 5 GB",
"id": "7ed5b6fe-abcf-4769-a9ea-180aa7240279",
"iscustomized": false,
"name": "Small",
"provisioningtype": "thin",
"storagetype": "shared"
},
{
"created": "2015-12-04T15:19:59+0000",
"disksize": 20,
"displayoffering": true,
"displaytext": "Medium Disk, 20 GB",
"id": "62f4cdf6-5d01-410c-9ca4-0addc9097229",
"iscustomized": false,
"name": "Medium",
"provisioningtype": "thin",
"storagetype": "shared"
},
{
"created": "2015-12-04T15:19:59+0000",
"disksize": 100,
"displayoffering": true,
"displaytext": "Large Disk, 100 GB",
"id": "4517e129-034c-4659-8b56-d8e19b5fb540",
"iscustomized": false,
"name": "Large",
"provisioningtype": "thin",
"storagetype": "shared"
}
]
}
```

Packer version: 0.12.2
CloudStack version: 4.8