XenAPIPlugin.py: Remove the superflous catch & raise of SystemExit

[ashwin9390]

When reviewing XAPIPlugin.py for warning fixes,

Bernhard found a superfluous catch and raise in XenAPIPlugin.py's dispatch() function
that we can clean up:

Commmit message:

SystemExit does not need to be caught and raised in this try:
Both other exceptions are subclasses of Exception, so they don't catch SystemExit(BaseException):

By design, SystemExit is a subclass of BaseException and because we are not catching BaseException and also not use a bare except: here, we can cleanup catching and re-raising SystemExit() here.
Reference: https://docs.python.org/3/library/exceptions.html#SystemExit

Author / Signed-off-by: Bernhard Kaindl bernhard.kaindl@cloud.com

Committed by: Signed-off-by: Ashwinh ashwin.h@cloud.com

[bernhardkaindl]

Thanks for opening and reviewing this PR. I wanted to add the reference:

https://docs.python.org/3/library/exceptions.html#SystemExit

Quote:

exception SystemExit
This exception is raised by the sys.exit() function.
It inherits from BaseException instead of Exception so that it is not accidentally caught by code that catches Exception.
This allows the exception to properly propagate up and cause the interpreter to exit.

Hence, as we are not catching BaseException (Failure is also a subclass of Exception) in this try (and we also are not using a bare except:, the SystemExit BaseException will traverse this try without getting chatched. Thus, catching and re-raising it is not needed.