Verify go version when building packer.

Check if the installed version is greater than the required version. Error out if that's not the case

scripts/devcompile.sh

@@ -8,6 +8,40 @@ OK_COLOR="\x1b[32;01m"
 ERROR_COLOR="\x1b[31;01m"
 WARN_COLOR="\x1b[33;01m"
 
+# http://stackoverflow.com/questions/4023830/bash-how-compare-two-strings-in-version-format
+verify_go () {
+    if [[ $1 == $2 ]]
+    then
+        return 0
+    fi
+    local IFS=.
+    local i ver1=($1) ver2=($2)
+
+    for ((i=${#ver1[@]}; i<${#ver2[@]}; i++))
+    do
+        ver1[i]=0
+    done
+    for ((i=0; i<${#ver1[@]}; i++))
+    do
+        if [[ -z ${ver2[i]} ]]
+        then
+            ver2[i]=0
+        fi
+        if ((10#${ver1[i]} > 10#${ver2[i]}))
+        then
+            echo -e "${ERROR_COLOR}==> Required Go version $1 not installed. Found $2 instead"
+            exit 1
+        fi
+    done
+}
+
+GO_MINIMUM_VERSION=1.2
+GO_INSTALLED_VERSION=$(go version | cut -d ' ' -f 3)
+GO_INSTALLED_VERSION=${GO_INSTALLED_VERSION#"go"}
+
+echo -e "${OK_COLOR}==> Verifying Go"
+verify_go $GO_MINIMUM_VERSION $GO_INSTALLED_VERSION
+
 # Get the parent directory of where this script is.
 SOURCE="${BASH_SOURCE[0]}"
 while [ -h "$SOURCE" ] ; do SOURCE="$(readlink "$SOURCE")"; done