Make zombienet tests native friendly (#6588)

* Make zombienet tests native friendly

* Update zombienet_tests/README.md

Co-authored-by: Bastian Köcher <info@kchr.de>

* Get rid of `{{ZOMBIENET_NATIVE_BINARY_PREFIX}}`

* Remove pointless changes

* add set_env helper and doc in readme

* changes from feedback

---------

Co-authored-by: Bastian Köcher <info@kchr.de>
Co-authored-by: Javier Viola <javier@parity.io>

polkadot/zombienet_tests/.set_env

@@ -0,0 +1,20 @@
+pathprepend() {
+  for ((i=$#; i>0; i--));
+  do
+    ARG="$@[$i]"
+    if [ -d "$ARG" ] && [[ ":$PATH:" != *":$ARG:"* ]]; then
+        PATH="$ARG${PATH:+":$PATH"}"
+    fi
+  done
+}
+
+# paths are prepend in order, so you can manage with version will run
+# by the order of this array
+CUSTOM_PATHS=(
+  "~/polkadot/target/release"
+  "~/polkadot/target/testnet"
+  "~/cumulus/target/release"
+)
+
+pathprepend $CUSTOM_PATHS
+export PATH=$PATH