Remove use of pkg_resources from osrf_pycommon.

Replace it with the use of the more modern importlib*
libraries.  There are a couple of reasons to do this:

1.  pkg_resources is quite slow to import; on my machine,
just firing up the python interpreter takes ~35ms, while
firing up the python interpreter and importing pkg_resources
takes ~175ms.  Firing up the python interpreter and importing
importlib_metadata takes ~70ms.  Removing 100ms per invocation
of the command-line both makes it speedier for users, and
will speed up our tests (which call out to the command-line
quite a lot).

2.  pkg_resources is somewhat deprecated and being replaced
by importlib.  https://importlib-metadata.readthedocs.io/en/latest/using.html
describes some of it

Signed-off-by: Chris Lalancette <[email protected]>

.travis.yml

@@ -6,7 +6,7 @@ python:
   - "3.7"
   - "3.8"
 install:
-  - pip install coverage nose flake8 mock
+  - pip install coverage nose flake8 mock importlib-metadata
   - pip install git+https://github.com/PyCQA/flake8-import-order.git
 script:
   - if [[ $TRAVIS_PYTHON_VERSION == 3* ]]; then COVER_INCLUSIVE=--cover-inclusive; fi

osrf_pycommon/cli_utils/verb_pattern.py

@@ -17,7 +17,7 @@
 import sys
 import inspect
 
-import pkg_resources
+import importlib_metadata
 
 
 def call_prepare_arguments(func, parser, sysargs=None):
@@ -149,7 +149,7 @@ def list_verbs(group):
     :rtype: list of str
     """
     verbs = []
-    for entry_point in pkg_resources.iter_entry_points(group=group):
+    for entry_point in importlib_metadata.entry_points().get(group, []):
         verbs.append(entry_point.name)
     return verbs
 
@@ -162,7 +162,7 @@ def load_verb_description(verb_name, group):
     :returns: verb description
     :rtype: dict
     """
-    for entry_point in pkg_resources.iter_entry_points(group=group):
+    for entry_point in importlib_metadata.entry_points().get(group, []):
         if entry_point.name == verb_name:
             return entry_point.load()
 

package.xml

@@ -12,6 +12,7 @@
 
   <exec_depend condition="$ROS_PYTHON_VERSION == 2">python-mock</exec_depend>
   <exec_depend condition="$ROS_PYTHON_VERSION == 3">python3-mock</exec_depend>
+  <exec_depend condition="$ROS_PYTHON_VERSION == 3">python3-importlib-metadata</exec_depend>
 
   <export>
     <build_type>ament_python</build_type>