Add single retry for dotnet-install.sh

Author: HaoK

test/vstest/runtests.sh

@@ -1,6 +1,13 @@
 #!/usr/bin/env bash
-curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin --version $2 --no-cdn --install-dir $HELIX_CORRELATION_PAYLOAD/sdk
-curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin --runtime dotnet --version $3 --no-cdn --install-dir $HELIX_CORRELATION_PAYLOAD/sdk
+curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin --version $2 --install-dir $HELIX_CORRELATION_PAYLOAD/sdk
+if [ $retVal -ne 0 ]; then 
+    curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin --version $2 --install-dir $HELIX_CORRELATION_PAYLOAD/sdk
+fi
+curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin --runtime dotnet --version $3 --install-dir $HELIX_CORRELATION_PAYLOAD/sdk
+if [ $retVal -ne 0 ]; then 
+    curl -sSL https://dot.net/v1/dotnet-install.sh | bash /dev/stdin --runtime dotnet --version $3 --install-dir $HELIX_CORRELATION_PAYLOAD/sdk
+fi
+
 export DOTNET_SKIP_FIRST_TIME_EXPERIENCE=1
 
 # Ensures every invocation of dotnet apps uses the same dotnet.exe