Fix last remaining test on Android (#2457)

Motivation

Get all tests passing on Android AArch64

Modifications

- Check if localhost is set for IPv6 in BootstrapTest/testClientBindWorksOnSocketsBoundToEitherIPv4OrIPv6Only,
  and use ip6-localhost if not

Result

All tests pass natively on Android AArch64

Tests/NIOPosixTests/BootstrapTest.swift

@@ -644,10 +644,21 @@ class BootstrapTest: XCTestCase {
 
             var maybeChannel1: Channel? = nil
             // Try 2: Connect to "localhost", this will do Happy Eyeballs.
+            var localhost = "localhost"
+            // Some platforms don't define "localhost" for IPv6, so check that
+            // and use "ip6-localhost" instead.
+            if !isIPv4 {
+                let hostResolver = GetaddrinfoResolver(loop: group.next(), aiSocktype: .stream, aiProtocol: .tcp)
+                let hostv6 = try! hostResolver.initiateAAAAQuery(host: "localhost", port: 8088).wait()
+                if hostv6.isEmpty {
+                    localhost = "ip6-localhost"
+                }
+            }
+
             XCTAssertNoThrow(maybeChannel1 = try ClientBootstrap(group: self.group)
                                 .channelOption(ChannelOptions.socketOption(.so_reuseaddr), value: 1)
                                 .bind(to: clientLocalAddressWholeInterface)
-                                .connect(host: "localhost", port: server1LocalAddress.port!)
+                                .connect(host: localhost, port: server1LocalAddress.port!)
                                 .wait())
             guard let myChannel1 = maybeChannel1, let myChannel1Address = myChannel1.localAddress else {
                 XCTFail("can't connect channel 1")