bugfix: prevent duplicate connections in pool

An user can specify duplicate addresses in ConnectionPool. We cannot
support multiple connections to the same address due to
ConnectionPool.GetPoolInfo() implementation without breaking backward
compatibility. So we need to skip duplicates.

Closes #208

Author: oleg-jukovec

connection_pool/connection_pool.go

@@ -97,7 +97,7 @@ func ConnectWithOpts(addrs []string, connOpts tarantool.Opts, opts OptsPool) (co
 	anyPool := NewEmptyRoundRobin(size)
 
 	connPool = &ConnectionPool{
-		addrs:    make([]string, len(addrs)),
+		addrs:    make([]string, 0, len(addrs)),
 		connOpts: connOpts,
 		opts:     opts,
 		notify:   notify,
@@ -107,7 +107,14 @@ func ConnectWithOpts(addrs []string, connOpts tarantool.Opts, opts OptsPool) (co
 		roPool:   roPool,
 		anyPool:  anyPool,
 	}
-	copy(connPool.addrs, addrs)
+
+	m := make(map[string]bool)
+	for _, addr := range addrs {
+		if _, ok := m[addr]; !ok {
+			m[addr] = true
+			connPool.addrs = append(connPool.addrs, addr)
+		}
+	}
 
 	somebodyAlive := connPool.fillPools()
 	if !somebodyAlive {

connection_pool/connection_pool_test.go

@@ -80,6 +80,31 @@ func TestConnSuccessfully(t *testing.T) {
 	require.Nil(t, err)
 }
 
+func TestConnSuccessfullyDuplicates(t *testing.T) {
+	server := servers[0]
+	connPool, err := connection_pool.Connect([]string{server, server, server, server}, connOpts)
+	require.Nilf(t, err, "failed to connect")
+	require.NotNilf(t, connPool, "conn is nil after Connect")
+
+	defer connPool.Close()
+
+	args := test_helpers.CheckStatusesArgs{
+		ConnPool:           connPool,
+		Mode:               connection_pool.ANY,
+		Servers:            []string{server},
+		ExpectedPoolStatus: true,
+		ExpectedStatuses: map[string]bool{
+			server: true,
+		},
+	}
+
+	err = test_helpers.CheckPoolStatuses(args)
+	require.Nil(t, err)
+
+	addrs := connPool.GetAddrs()
+	require.Equalf(t, []string{server}, addrs, "should be only one address")
+}
+
 func TestReconnect(t *testing.T) {
 	server := servers[0]