Fix for genjava ignoring most packages in standalone mode

The genjava_message_artifacts tool in package genjava calls rosjava_build_tools.catkin.index_message_package_dependencies_from_local_environment()
to generate a list of all message packages and their dependencies in topological order from the list of package names given in the command line.

Especially in cases where ROS_PACKAGE_PATH lists the package paths for each individual package separately, which is the case in isolated
builds using catkin_make_isolated or catkin_tools, the relative path returned by catkin_pkg.packages.find_packages() is only `.`. In general, the
relative package path is not unique, but it is used as key of a dictionary when passed to topological_order_packages a few lines below.
As a consequence, all packages but one of each group that have the same relative package path were missing in the returned list and hence no
artifacts were generated by genjava_message_artifacts.

This patch adds a line that transforms the relative to the absolute package path, avoiding the above problem.

Author: meyerj

src/rosjava_build_tools/catkin.py

@@ -52,6 +52,8 @@ def index_message_package_dependencies_from_local_environment(package_name_list=
     # i.e. no duplicates!
     for path in reversed(package_paths):
         for package_path, package in catkin_pkg.packages.find_packages(path).items():
+            # resolve and normalize absolute path because it is used as a key below
+            package_path = os.path.normpath(os.path.join(path, package_path))
             all_packages[package.name] = (package_path, package)
             if has_build_depend_on_message_generation(package) or package.name in message_package_whitelist:
                 if package_name_list: