[mc] Add python package and improve Forge install robustness

For #148

minecraft-server/Dockerfile

@@ -15,7 +15,8 @@ RUN echo "http://dl-3.alpinelinux.org/alpine/v3.5/community/" >> /etc/apk/reposi
           curl \
           git \
           jq \
-          mysql-client &&\
+          mysql-client \
+          python python-dev && \
         rm -rf /var/cache/apk/*
 
 RUN addgroup -g 1000 minecraft \

minecraft-server/start-minecraft.sh

@@ -159,7 +159,17 @@ function installForge {
     echo "Downloading $FORGE_INSTALLER ..."
     wget -q $downloadUrl
     echo "Installing $SERVER"
-    java -jar $FORGE_INSTALLER --installServer
+    tries=3
+    while ((--tries >= 0)); do
+      java -jar $FORGE_INSTALLER --installServer
+      if [ $? == 0 ]; then
+        break
+      fi
+    done
+    if (($tries < 0)); then
+      echo "Forge failed to install after several tries." >&2
+      exit 10
+    fi
   fi
 }