avocado..tree: Support for getting node by path

This function can be used to retrieve existing node by path separated
by '/'. Additionally when "create" is supplied it it can create the
missing nodes in the same way as "mkdir -p" in bash.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/tree.py

@@ -248,6 +248,29 @@ class TreeNode(object):
             child.set_environment_dirty()
         self._environment = None
 
+    def get_node(self, path, create=False):
+        """
+        :param path: Path of the desired node (relative to this node)
+        :param create: Create the node (and intermediary ones) when not present
+        :return: the node associated with this path
+        :raise ValueError: When path doesn't exist and create not set
+        """
+        node = self
+        for name in path.split('/'):
+            if not name:
+                continue
+            try:
+                node = node.children[node.children.index(name)]
+            except ValueError:
+                if create:
+                    child = node.__class__(name)
+                    node.add_child(child)
+                    node = child
+                else:
+                    raise ValueError("Path %s does not exists in this tree\n%s"
+                                     % (path, self.get_ascii()))
+        return node
+
     def iter_children_preorder(self):
         """ Iterate through children """
         queue = collections.deque()