swift 5 docker support (#952)

* swift 5 docker support

Motivation: easily build and test swift-nio v1 using swift 5 docker

Modifications: adjust dockerfile and add docker-compose file for ubuntu 18.04, swift 5

docker/Dockerfile

@@ -51,8 +51,10 @@ RUN gem install jazzy --no-ri --no-rdoc
 # swift
 ARG swift_version=4.0.3
 ARG swift_flavour=RELEASE
+ARG swift_builds_suffix=release
+
 RUN mkdir $HOME/.swift
-RUN wget -q https://swift.org/builds/swift-${swift_version}-$(echo $swift_flavour | tr A-Z a-z)/ubuntu$(echo $ubuntu_version | sed 's/\.//g')/swift-${swift_version}-${swift_flavour}/swift-${swift_version}-${swift_flavour}-ubuntu${ubuntu_version}.tar.gz -O $HOME/swift.tar.gz
+RUN wget -q "https://swift.org/builds/swift-${swift_version}-${swift_builds_suffix}/ubuntu$(echo $ubuntu_version | sed 's/\.//g')/swift-${swift_version}-${swift_flavour}/swift-${swift_version}-${swift_flavour}-ubuntu${ubuntu_version}.tar.gz" -O $HOME/swift.tar.gz
 RUN tar xzf $HOME/swift.tar.gz --directory $HOME/.swift --strip-components=1
 RUN echo 'export PATH="$HOME/.swift/usr/bin:$PATH"' >> $HOME/.profile
 RUN echo 'export LINUX_SOURCEKIT_LIB_PATH="$HOME/.swift/usr/lib"' >> $HOME/.profile

docker/docker-compose.1804.50.yaml

@@ -0,0 +1,26 @@
+version: "3"
+
+services:
+
+  runtime-setup:
+    image: swift-nio:18.04-5.0
+    build:
+      args:
+        ubuntu_version: "18.04"
+        swift_version: "5.0"
+        skip_ruby_from_ppa: "true"
+
+  unit-tests:
+    image: swift-nio:18.04-5.0
+
+  integration-tests:
+    image: swift-nio:18.04-5.0
+
+  test:
+    image: swift-nio:18.04-5.0
+
+  echo:
+    image: swift-nio:18.04-5.0
+
+  http:
+    image: swift-nio:18.04-5.0