Still fixing for cookiecutter-based plugins

nldi-xstool was migrated to be a cookiecutter based plugin, and as such it doesn't quite conform to the process it used to need in order to be built. Notably, there is no setup.py file, which requires pip to use a special command-line option to use PEP-517 based projects that have replaced setup.py with pyproject.toml. The new cookiecutter plugins also rely on Python 3.9, however the Ubuntu version we need for gdal to be able to be installed only supports Python 3.8 directly. So the docker image had to be modified to install Python 3.9 using pyenv. Futher adjustments to ensure the correct and expected versions of modules are installed were also required.

Finally -- there was an issue that if a plugin didn't build correctly, the Docker image would still continue building as if everything was fine. This was not a desired outcome. As such, the script that the pygeoapi-plugins module builds now adds || exit $? at the end of the pip installs for each plugin repo. The script will now error out correctly if pip errors on those installs.

Signed-off-by: Cliff Hill chill@contractor.usgs.gov