Fix QNetworkReply ServiceUnavailableError in macOS

For macOS and Windows, the test-server containers are deployed in the
VirtualBox (Boot2Docker). Because Boot2Docker is a lightweight Linux
distribution made specifically to run Docker containers, it doesn't
install avahi-daemon and support mDNS discovery.

To resolve this problem, Docker compose file supports "extra_hosts" to
add hostname mappings inside containers.

BFAIL items:
tst_QNetworkReply::headFromHttp(...+proxy...) (ten cases)
tst_QNetworkReply::ioGetWithManyProxies(http-on-http)
tst_QNetworkReply::ioGetWithManyProxies(http-on-http2)
tst_QNetworkReply::ioGetWithManyProxies(http-on-multiple-http)
tst_QNetworkReply::ioGetWithManyProxies(http-on-http+socks)
tst_QNetworkReply::ioGetWithManyProxies(http-on-ftp+http+socks)
tst_QNetworkReply::ioPostToHttpFromSocket(...+proxy) (twelve cases)
tst_QNetworkReply::ioPostToHttpFromSocket(...+proxyauth) (ten cases)

Change-Id: Iec55966a9b5f191b7446985a15b49a8b09dcf407
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>

tests/testserver/docker-compose-for-macOS.yml

@@ -21,6 +21,8 @@ services:
         entrypoint: common/startup.sh
         command: [common/ssl.sh, service/apache2.sh]
         network_mode: "host"
+        extra_hosts:
+            - "qt-test-server.${TEST_DOMAIN}:${MACHINE_IP}"
         environment:
             - test_domain=${TEST_DOMAIN}
 
@@ -36,6 +38,8 @@ services:
         entrypoint: common/startup.sh
         command: service/squid.sh
         network_mode: "host"
+        extra_hosts:
+            - "qt-test-server.${TEST_DOMAIN}:${MACHINE_IP}"
         environment:
             - test_domain=${TEST_DOMAIN}
 
@@ -49,6 +53,8 @@ services:
         entrypoint: common/startup.sh
         command: service/vsftpd.sh
         network_mode: "host"
+        extra_hosts:
+            - "qt-test-server.${TEST_DOMAIN}:${MACHINE_IP}"
         environment:
             - test_domain=${TEST_DOMAIN}
 
@@ -64,6 +70,8 @@ services:
         entrypoint: common/startup.sh
         command: service/ftp-proxy.sh
         network_mode: "host"
+        extra_hosts:
+            - "qt-test-server.${TEST_DOMAIN}:${MACHINE_IP}"
         environment:
             - test_domain=${TEST_DOMAIN}
 
@@ -81,6 +89,8 @@ services:
         entrypoint: common/startup.sh
         command: service/danted.sh
         network_mode: "host"
+        extra_hosts:
+            - "qt-test-server.${TEST_DOMAIN}:${MACHINE_IP}"
         environment:
             - danted_internal=${MACHINE_IP:-eth0}
             - danted_external=${MACHINE_IP:-eth0}