Extract function for launching httpbin into its own file

Allow reusing it between GitHub and Travis CI.

Also show httpbin log in Travis CI logs too, not just on GitHub.

build/tools/httpbin.sh

@@ -0,0 +1,44 @@
+# This script is sourced by CI scripts to launch httpbin.
+#
+# Do not run it directly.
+
+httpbin_launch() {
+    echo 'Launching httpbin...'
+
+    case "$(uname -s)" in
+        Linux)
+            dist_codename=$(lsb_release --codename --short)
+            ;;
+    esac
+
+    # We need to disable SSL certificate checking under Trusty because Python
+    # version there is too old to support SNI.
+    case "$dist_codename" in
+        trusty)
+            # Here "decorator==4.4.2" doesn't work neither for some reason ("no
+            # matching distribution found"), so use an explicit URL.
+            pip_decorator_arg='https://files.pythonhosted.org/packages/ed/1b/72a1821152d07cf1d8b6fce298aeb06a7eb90f4d6d41acec9861e7cc6df0/decorator-4.4.2-py2.py3-none-any.whl'
+            pip_options='--trusted-host files.pythonhosted.org'
+            ;;
+
+        *)
+            # Current decorator (>= 5) is incompatible with Python 2 which we
+            # still use under in some builds, so explicitly use a version which
+            # is known to work.
+            pip_decorator_arg='decorator==4.4.2'
+            ;;
+    esac
+
+    pip install $pip_decorator_arg httpbin --user $pip_options
+    python -m httpbin.core 2>&1 >httpbin.log &
+    WX_TEST_WEBREQUEST_URL="http://localhost:5000"
+
+    export WX_TEST_WEBREQUEST_URL
+}
+
+httpbin_show_log() {
+    echo '*** Tests failed, contents of httpbin.log follows: ***'
+    echo '-----------------------------------------------------------'
+    cat httpbin.log
+    echo '-----------------------------------------------------------'
+}