test: Use loop devices in TestStorageMdRaid on C9S

Mixing scsi_debug and loop does strange things on CentOS 9 Testing Farm
instances, and the SCSI disk doesn't get detected properly as part of
the array.

This papers over a bug, but we are testing the Cockpit logic here, not
weird low-level kernel bugs. See #22143 for debug information.

Cherry-picked from main commit cdf678a

Author: martinpitt

test/verify/check-storage-mdraid

@@ -80,7 +80,12 @@ class TestStorageMdRaid(storagelib.StorageCase):
         self.login_and_go("/storage")
 
         # Add four disks and make a RAID out of three of them
-        disk1 = self.add_ram_disk()
+        # HACK: on CentOS 9 (only!), scsi_debug doesn't like being part of a RAID
+        # see https://github.com/cockpit-project/cockpit/pull/22143
+        if m.image.startswith('centos-9'):
+            disk1 = self.add_loopback_disk(name="loop4")
+        else:
+            disk1 = self.add_ram_disk()
         b.wait_visible(self.card_row("Storage", name=disk1))
         disk2 = self.add_loopback_disk(name="loop5")
         b.wait_visible(self.card_row("Storage", name=disk2))
@@ -272,7 +277,12 @@ class TestStorageMdRaid(storagelib.StorageCase):
 
         self.login_and_go("/storage")
 
-        disk1 = self.add_ram_disk()
+        # HACK: on CentOS 9 (only!), scsi_debug doesn't like being part of a RAID
+        # see https://github.com/cockpit-project/cockpit/pull/22143
+        if m.image.startswith('centos-9'):
+            disk1 = self.add_loopback_disk()
+        else:
+            disk1 = self.add_ram_disk()
         b.wait_visible(self.card_row("Storage", name=disk1))
         disk2 = self.add_loopback_disk()
         b.wait_visible(self.card_row("Storage", name=disk2))