PerfMonComps: Enable flake8

This MR is a follow-up to !38852 (merged) and relates to ATEAM-678. We're enabling flake8 for the python modules and scripts under Control/PerformanceMonitoring/PerfMonComps. No new functionality is introduced. There is a minor bug-fix in the way PerfMonSvc obtains the list of algorithms. For example, in q431 the number of algorithms running were being reported to be zero:

Py:PerfMonSvc        INFO job had [0] algorithms

now this is corrected:

Py:PerfMonSvc        INFO job had [377] algorithms