added more use cases for xml

tests/variableTreeXml/cherryPick.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<device_server xmlns="https://github.com/ChimeraTK/ControlSystemAdapter-DoocsAdapter">
+  <location name="DIRECT">
+    <property source="/A/b/do"/>
+    <property source="INT"/>
+  </location>
+</device_server>

tests/variableTreeXml/importAll.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<device_server xmlns="https://github.com/ChimeraTK/ControlSystemAdapter-DoocsAdapter">
+  <import>/</import>
+</device_server>

tests/variableTreeXml/importAndRename.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<device_server xmlns="https://github.com/ChimeraTK/ControlSystemAdapter-DoocsAdapter">
+  <location name="DIRECT">
+    <property source="INT" name="FOO"/>
+    <property source="/DIRECT/DOUBLE" name="BAR"/>
+    <import>/DIRECT</import>
+  </location>
+</device_server>

tests/variableTreeXml/importLocation.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<device_server xmlns="https://github.com/ChimeraTK/ControlSystemAdapter-DoocsAdapter">
+  <location name="B">
+    <import>/A</import>
+  </location>
+</device_server>