Find pip-compile in global path if it does not exist in venv

[furushchev]

This PR modifies the script to locate and execute pip-compile from the global path if it is not found within the current virtual environment.

Currently, the script assumes that pip-compile is installed within the activated virtual environment. However, users may have pip-compile installed globally and installer does not install the pip-tools to the venv space in the case [1].

This change allows the script to search for `pip-compile in the system's PATH if it's not found in the virtual environment's bin directory.

[1] Such users will see the error:

Traceback (most recent call last):
  File "/home/furushchev/catkin_ws/devel/lib/catkin_virtualenv/venv_lock", line 15, in <module>
    exec(compile(fh.read(), python_script, 'exec'), context)
  File "/home/furushchev/catkin_ws/src/catkin_virtualenv/catkin_virtualenv/scripts/venv_lock", line 47, in <module>
    venv.lock(
  File "/home/furushchev/catkin_ws/src/catkin_virtualenv/catkin_virtualenv/src/catkin_virtualenv/venv.py", line 159, in lock
    pip_compile = self._venv_bin("pip-compile")
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/furushchev/catkin_ws/src/catkin_virtualenv/catkin_virtualenv/src/catkin_virtualenv/venv.py", line 195, in _venv_bin
    raise RuntimeError("Binary {} not found in venv".format(binary_name))
RuntimeError: Binary pip-compile not found in venv
make[2]: *** [CMakeFiles/sound_classification_generate_virtualenv.dir/build.make:97: /home/furushchev/catkin_ws/src/jsk_recognition/sound_classification/requirements.txt] Error 1
make[1]: *** [CMakeFiles/Makefile2:788: CMakeFiles/sound_classification_generate_virtualenv.dir/all] Error 2
make: *** [Makefile:146: all] Error 2

$ locate pip-compile 
/usr/local/bin/pip-compile

[furushchev]

Just rebased origin/master.

[furushchev]

@paulbovbel Thank you for your review. Please let me know if there is any problem or further comment!

[furushchev]

@paulbovbel Hello! Is there any chance to get this PR merged soon?

[furushchev]

@paulbovbel Hello! Can you please merge this and release this package as the EOL of the ROS1 is coming soon 🙇