Fix doc errors in nimble driver documentation

Last update had some syntax errors that introduced warnings. This
passes in gate since the way that is currently run does not treat
warnings as errors, but when running locally via tox where we do
enforce this it fails.

Change-Id: Ib2a2e850a73c4f4c8afd56b372b5b4d7ba5ec47f

doc/source/configuration/block-storage/drivers/nimble-volume-driver.rst

@@ -163,12 +163,13 @@ Configuring mulitpathing varies by system depending on the environment. In a
 scenario where solely Nimble devices are being created by Cinder, the
 following ``/etc/multipath.conf`` file may be used:
 
-.. code-block:: json
+.. code-block:: text
 
    defaults {
        user_friendly_names yes
        find_multipaths     no
    }
+
    blacklist {
        devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
        devnode "^hd[a-z]"
@@ -177,12 +178,14 @@ following ``/etc/multipath.conf`` file may be used:
            product ".*"
        }
    }
+
    blacklist_exceptions {
        device {
            vendor  "Nimble"
            product "Server"
        }
    }
+
    devices {
        device {
            vendor               "Nimble"
@@ -243,4 +246,5 @@ To validate that instances get properly connected to the multipath device,
 inspect the instance devices:
 
 .. code-block:: console
+
    # virsh dumpxml <Instance ID | Instance Name | Instance UUID>