Use python `logging` module for `util.log()`, separate into log levels

[comps]

The lib.util.log code can be modified to look like atex/util/log.py to be usable natively with Python's logging module, and then split into multiple functions like util.debug(), util.info(), util.warning(), etc.

This is very useful for multiple levels of verbosity, allowing us to run with ie. info or warning during large productization runs, but override that with debug when debugging a single test.

This would allow us to see fine details like ssh key generation, virsh executions for starting up VMs, systemctl commands to query a service, etc. ... For example, the util.subprocess_* functions could take loglevel= argument rather than being "verbose vs silent" as now.

The code to set up console logging would be in lib/runtest.py and look like

logging.basicConfig(
    level=logging.INFO,
    stream=sys.stderr,
    format='%(asctime)s %(name)s: %(message)s',
    datefmt='%Y-%m-%d %H:%M:%S',
)

(to simulate the output format we have now)

In that example, logging.INFO could come from some CONTEST_LOGLEVEL env var, or something like that, again checked in lib/runtest.py to avoid extra test code.

[comps]

This would also let us see debug messages from other modules, ie. requests, when using logging.DEBUG, so we would see HTTP requests, etc.

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There are some ideas I implemented (or plan to implement) in ATEX that might be releant here, specifically:

• Not prefixing full file/class/function/linenr to all logged messages if loglevel is >= INFO. This avoids noise when running the test manually from CLI, but allows saving full DEBUG log separately (something I plan to do in ATEX).
  • Not sure if super useful for Contest
• Replacing the skip_frames= logic for a hardcoded list of "unwind" paths, defined in util/log.py. Basically if a file.class.function (or something like that) matches some "known bad" list like util.subprocess_run, unwind it by 1 stack level. Continue doing so until the stack level doesn't match anything in the "unwind" list.
  • In ATEX, I want to do this to maintain API compatibility of various functions (like util.subprocess_run) with the official python subprocess module and its functions, but I think it's not a bad idea for Contest either.

Maybe wait with this issue until ^^^ is implemented in ATEX, and then we can copy/paste it.

[comps]

This has been done a few months ago in ATEX: https://github.com/RHSecurityCompliance/atex/blob/af9b0d9744dbda74ff414b0de72be058f5414373/atex/util/log.py

The current (very latest as of today) implementation in ATEX doesn't use it anymore, as it relies solely on logging natively, but we shouldn't do that in Contest. Instead, get inspired by the link above (abstracting skip_frames into the log.py file).