Make schem agreement query pull only columns that are used

Currently schema agreement logic run `select * from system.peers`, while
only `schema_version` is used, it creates excessive load on cluster and
driver side.

Author: dkropachev

core/src/main/java/com/datastax/oss/driver/internal/core/metadata/SchemaAgreementChecker.java

@@ -108,7 +108,7 @@ private void sendQueries() {
     } else {
       CompletionStage<AdminResult> localQuery =
           query("SELECT schema_version FROM system.local WHERE key='local'");
-      CompletionStage<AdminResult> peersQuery = query("SELECT * FROM system.peers");
+      CompletionStage<AdminResult> peersQuery = query("SELECT schema_version FROM system.peers");
 
       localQuery
           .thenCombine(peersQuery, this::extractSchemaVersions)

core/src/test/java/com/datastax/oss/driver/internal/core/metadata/SchemaAgreementCheckerTest.java

@@ -139,7 +139,7 @@ public void should_succeed_if_only_one_node() {
         new StubbedQuery(
             "SELECT schema_version FROM system.local WHERE key='local'",
             mockResult(mockLocalRow(VERSION1))),
-        new StubbedQuery("SELECT * FROM system.peers", mockResult(/*empty*/ )));
+        new StubbedQuery("SELECT schema_version FROM system.peers", mockResult(/*empty*/ )));
 
     // When
     CompletionStage<Boolean> future = checker.run();
@@ -156,7 +156,8 @@ public void should_succeed_if_versions_match_on_first_try() {
         new StubbedQuery(
             "SELECT schema_version FROM system.local WHERE key='local'",
             mockResult(mockLocalRow(VERSION1))),
-        new StubbedQuery("SELECT * FROM system.peers", mockResult(mockValidPeerRow(VERSION1))));
+        new StubbedQuery(
+            "SELECT schema_version FROM system.peers", mockResult(mockValidPeerRow(VERSION1))));
 
     // When
     CompletionStage<Boolean> future = checker.run();
@@ -174,7 +175,8 @@ public void should_ignore_down_peers() {
         new StubbedQuery(
             "SELECT schema_version FROM system.local WHERE key='local'",
             mockResult(mockLocalRow(VERSION1))),
-        new StubbedQuery("SELECT * FROM system.peers", mockResult(mockValidPeerRow(VERSION2))));
+        new StubbedQuery(
+            "SELECT schema_version FROM system.peers", mockResult(mockValidPeerRow(VERSION2))));
 
     // When
     CompletionStage<Boolean> future = checker.run();
@@ -210,7 +212,7 @@ public void should_ignore_malformed_rows(AdminRow malformedPeer) {
         new StubbedQuery(
             "SELECT schema_version FROM system.local WHERE key='local'",
             mockResult(mockLocalRow(VERSION1))),
-        new StubbedQuery("SELECT * FROM system.peers", mockResult(malformedPeer)));
+        new StubbedQuery("SELECT schema_version FROM system.peers", mockResult(malformedPeer)));
 
     // When
     CompletionStage<Boolean> future = checker.run();
@@ -228,13 +230,15 @@ public void should_reschedule_if_versions_do_not_match_on_first_try() {
         new StubbedQuery(
             "SELECT schema_version FROM system.local WHERE key='local'",
             mockResult(mockLocalRow(VERSION1))),
-        new StubbedQuery("SELECT * FROM system.peers", mockResult(mockValidPeerRow(VERSION2))),
+        new StubbedQuery(
+            "SELECT schema_version FROM system.peers", mockResult(mockValidPeerRow(VERSION2))),
 
         // Second round
         new StubbedQuery(
             "SELECT schema_version FROM system.local WHERE key='local'",
             mockResult(mockLocalRow(VERSION1))),
-        new StubbedQuery("SELECT * FROM system.peers", mockResult(mockValidPeerRow(VERSION1))));
+        new StubbedQuery(
+            "SELECT schema_version FROM system.peers", mockResult(mockValidPeerRow(VERSION1))));
 
     // When
     CompletionStage<Boolean> future = checker.run();
@@ -253,7 +257,8 @@ public void should_fail_if_versions_do_not_match_after_timeout() {
         new StubbedQuery(
             "SELECT schema_version FROM system.local WHERE key='local'",
             mockResult(mockLocalRow(VERSION1))),
-        new StubbedQuery("SELECT * FROM system.peers", mockResult(mockValidPeerRow(VERSION1))));
+        new StubbedQuery(
+            "SELECT schema_version FROM system.peers", mockResult(mockValidPeerRow(VERSION1))));
 
     // When
     CompletionStage<Boolean> future = checker.run();