Add NovaMaxDiskDevicesToAttach parameter

This change exposes the `[compute]/max_disk_devices_to_attach`
in Nova config. The paramerer sets maximum number of disk devices
allowed to attach to a single server.

Depends-On: https://review.opendev.org/708666
Change-Id: I08c5769bfe5f38d2503ed232b3771f615c24d158

deployment/nova/nova-compute-container-puppet.yaml

@@ -382,6 +382,23 @@ parameters:
     default: 0.0
     tags:
       - role_specific
+  NovaMaxDiskDevicesToAttach:
+    type: number
+    description: >
+      Maximum number of disk devices allowed to attach to a single server.
+      Note that the number of disks supported by an server depends
+      on the bus used. For example, the ide disk bus is limited to 4 attached
+      devices. The configured maximum is enforced during server create,
+      rebuild, evacuate, unshelve, live migrate, and attach volume.
+      Operators changing this parameter on a compute service that is hosting
+      servers should be aware that it could cause rebuilds to fail, if the
+      maximum is decreased lower than the number of devices already attached
+      to servers. Operators should also be aware that during a cold migration,
+      the configured maximum is only enforced in-place and the destination
+      is not checked before the move. -1 means unlimited
+    default: -1
+    tags:
+      - role_specific
 
   # DEPRECATED: the following options are deprecated and are currently maintained
   # for backwards compatibility. They will be removed in future release.
@@ -478,6 +495,7 @@ resources:
               nova::cpu_allocation_ratio: NovaCPUAllocationRatio
               nova::ram_allocation_ratio: NovaRAMAllocationRatio
               nova::disk_allocation_ratio: NovaDiskAllocationRatio
+              nova::compute::max_disk_devices_to_attach: NovaMaxDiskDevicesToAttach
             - values: {get_param: [RoleParameters]}
           - values:
               NovaVcpuPinSet: {get_param: NovaVcpuPinSet}
@@ -549,6 +567,7 @@ resources:
               NovaCPUAllocationRatio: {get_param: NovaCPUAllocationRatio}
               NovaRAMAllocationRatio: {get_param: NovaRAMAllocationRatio}
               NovaDiskAllocationRatio: {get_param: NovaDiskAllocationRatio}
+              NovaMaxDiskDevicesToAttach: {get_param: NovaMaxDiskDevicesToAttach}
 
 conditions:
   enable_instance_ha: {equals: [{get_param: EnableInstanceHA}, true]}

releasenotes/notes/add_max_disk_devices_to_attach-e219429d61a64bb0.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Adds `NovaMaxDiskDevicesToAttach` parameter that controls
+    `compute/max_disk_devices_to_attach` parameter in Nova.
+    This parameter sets maximum number of disk devices allowed
+    to attach to a single server.