software/kvm: fix json schemas

string.format must be a string according to
https://json-schema.org/understanding-json-schema/reference/string.html#format

We were using our own version of metaschema with a patch for this. Now
we are back to using official schema, but with a custom format
`internet-address` that should be equivalent to:

    "oneOf": [
      {
	"format": "hostname"
      },
      {
	"format": "ipv4"
      },
      {
	"format": "ipv6"
      }
    ],

software/kvm/instance-kvm-cluster-input-schema.json

@@ -368,11 +368,7 @@
               "title": "NBD hostname or IP",
               "description": "hostname (or IP) of the NBD server containing the boot image.",
               "type": "string",
-              "format": [
-                "host-name",
-                "ip-address",
-                "ipv6"
-              ],
+              "format": "internet-address",
               "default": "debian.nbd.vifib.net"
             },
             "nbd-port": {

software/kvm/instance-kvm-cluster-simplified-input-schema.json

@@ -64,11 +64,7 @@
               "title": "NBD hostname or IP",
               "description": "hostname (or IP) of the NBD server containing the boot image.",
               "type": "string",
-              "format": [
-                "host-name",
-                "ip-address",
-                "ipv6"
-              ],
+              "format": "internet-address",
               "default": "debian.nbd.vifib.net"
             },
             "nbd-port": {

software/kvm/instance-kvm-input-schema.json

@@ -172,11 +172,7 @@
       "title": "NBD hostname",
       "description": "hostname (or IP) of the NBD server containing the boot image.",
       "type": "string",
-      "format": [
-        "host-name",
-        "ip-address",
-        "ipv6"
-      ],
+      "format": "internet-address",
       "default": "debian.nbd.vifib.net"
     },
     "nbd-port": {
@@ -191,11 +187,7 @@
       "title": "Second NBD hostname",
       "description": "hostname (or IP) of the second NBD server (containing drivers for example).",
       "type": "string",
-      "format": [
-        "host-name",
-        "ip-address",
-        "ipv6"
-      ]
+      "format": "internet-address"
     },
     "nbd2-port": {
       "title": "Second NBD port",