vswitchd: Add unique indexes for some columns.

This is mainly intended to make life easier for database clients that don't
already have code to avoid creating records with duplicate names in various
OVS database tables.  With this commit, the database server itself rejects
attempts to add Port or Interface records with duplicate names or
Controller or Manager records with duplicate targets.

vswitchd/vswitch.ovsschema

@@ -1,6 +1,6 @@
 {"name": "Open_vSwitch",
- "version": "4.0.0",
- "cksum": "2606080158 14328",
+ "version": "5.0.0",
+ "cksum": "456700307 14434",
  "tables": {
    "Open_vSwitch": {
      "columns": {
@@ -92,7 +92,8 @@
          "type": {"key": {"type": "integer",
                           "minInteger": 0,
                           "maxInteger": 4095},
-                  "min": 0, "max": 4096}}}},
+                  "min": 0, "max": 4096}}},
+     "indexes": [["name"]]},
    "Port": {
      "columns": {
        "name": {
@@ -138,7 +139,8 @@
        "other_config": {
          "type": {"key": "string", "value": "string", "min": 0, "max": "unlimited"}},
        "external_ids": {
-         "type": {"key": "string", "value": "string", "min": 0, "max": "unlimited"}}}},
+         "type": {"key": "string", "value": "string", "min": 0, "max": "unlimited"}}},
+     "indexes": [["name"]]},
    "Interface": {
      "columns": {
        "name": {
@@ -208,7 +210,8 @@
          "ephemeral": true},
        "mtu": {
          "type": {"key": "integer", "min": 0, "max": 1},
-         "ephemeral": true}}},
+         "ephemeral": true}},
+     "indexes": [["name"]]},
    "QoS": {
      "columns": {
        "type": {
@@ -241,8 +244,7 @@
        "name": {
          "type": "string"},
        "select_all": {
-         "type": "boolean"
-       },
+         "type": "boolean"},
        "select_src_port": {
          "type": {"key": {"type": "uuid",
                           "refTable": "Port",
@@ -376,7 +378,8 @@
          "ephemeral": true},
        "status": {
          "type": {"key": "string", "value": "string", "min": 0, "max": "unlimited"},
-         "ephemeral": true}}},
+         "ephemeral": true}},
+     "indexes": [["target"]]},
    "SSL": {
      "columns": {
        "private_key": {