apsbss IOC starter script example has wrong python directory

[prjemian]

Documentation for the apsbss_ioc.sh starter shell script has a fixed python version in the path for APSTOOLS (${BLUESKY}/lib/python3.7/site-packages/apstools). Ran into a problem today where python 3.8 was used.

Need to make this example script more robust.

[prjemian]

We can learn the full path to the installed apstools from the default python, such as:

$ python -c "import apstools; print(apstools.__file__)"
/share1/bluesky/conda_envs/bluesky_2020_9/lib/python3.8/site-packages/apstools/__init__.py
$ dirname `python -c "import apstools; print(apstools.__file__)"`
/share1/bluesky/conda_envs/bluesky_2020_9/lib/python3.8/site-packages/apstools

[prjemian]

To eliminate the backticks, try this alternative:

$ dirname $(python -c "import apstools; print(apstools.__file__)")