Fix retrieve unpackaged so it is usable in metadeploy (#3566)

retrieve unpackaged messes with the package_xml in init_options which
breaks its use in Metadeploy (because _init_options ends up being called
twice)

Re-write options so it is not overwriting the valid value with an
invalid one.

Co-authored-by: David Reed <[email protected]>
Co-authored-by: James Estevez <[email protected]>

cumulusci/tasks/salesforce/RetrieveUnpackaged.py

@@ -27,11 +27,10 @@ def _init_options(self, kwargs):
         super(RetrieveUnpackaged, self)._init_options(kwargs)
 
         if "package_xml" in self.options:
-            self.options["package_xml_path"] = self.options["package_xml"]
-            with open(self.options["package_xml_path"], "r") as f:
-                self.options["package_xml"] = f.read()
+            with open(self.options["package_xml"], "r") as f:
+                self.options["package_xml_content"] = f.read()
 
     def _get_api(self):
         return self.api_class(
-            self, self.options["package_xml"], self.options.get("api_version")
+            self, self.options["package_xml_content"], self.options.get("api_version")
         )