Silence warnings display by python unit tests

There were two categories of warnings being displayed, those related
to the xdist plugin, and those related to SQLAlchemy 2.0 migration.

The xdist plugin warnings are due to a bug in pytest-cov, see:
    pytest-dev/pytest-cov#557
We just ignore them entirely for now, as that issue seems to be quiet.

The SQLAlchemy 2.0 migration warnings have 2 sub-categories.  The
first being that `declarative_base` has moved modules, and that warning
is removed by using the proper import.

However, once that `declarative_base` warning is removed, one
encounters:

    .../pbench/server/database/models/datasets.py:875:
        RemovedIn20Warning: "Metadata" object is being merged into a
        Session along the backref cascade path for relationship
        "Dataset.metadatas"; in SQLAlchemy 2.0, this reverse cascade
        will not take place.  Set cascade_backrefs to False in either
        the relationship() or backref() function for the 2.0 behavior;
        or to set globally for the whole Session, set the future=True
        flag (Background on SQLAlchemy 2.0 at:
        https://sqlalche.me/e/b8d9)
            meta = Metadata(**kwargs)

Since we are no going to migrate to SQLAlchemy 2.0 any time soon, it
seemed appropriate to just use the big hammer and turn the warnings
off entirely.

exec-tests

@@ -153,7 +153,7 @@ if [[ "${subtst:-python}" == "python" ]]; then
 
     printf -- "\n\n\nRunning %s python3-based unit tests via pytest\n\n" "${major_list// /,}"
     _pbench_sources=$(python3 -c 'import inspect, pathlib, pbench; print(pathlib.Path(inspect.getsourcefile(pbench)).parent)')
-    PYTHONUNBUFFERED=True _PBENCH_COV_DIR="${_toxenvdir}/cov" ${_ECHO} _time pytest \
+    SQLALCHEMY_SILENCE_UBER_WARNING=1 PYTHONUNBUFFERED=True _PBENCH_COV_DIR="${_toxenvdir}/cov" ${_ECHO} _time pytest \
         --tb=native \
         ${pytest_jobs_arg} \
         --basetemp="${_toxenvdir}/tmp" \
@@ -226,7 +226,7 @@ if [[ "${major}" == "all" || "${major}" == "server" ]]; then
         server_arg=${1}
         shift
         posargs="${@}"
-        PYTHONUNBUFFERED=True PBENCH_SERVER=${server_arg} pytest --tb=native -v -s ${posargs} --pyargs pbench.test.functional.server
+        SQLALCHEMY_SILENCE_UBER_WARNING=1 PYTHONUNBUFFERED=True PBENCH_SERVER=${server_arg} pytest --tb=native -v -s ${posargs} --pyargs pbench.test.functional.server
         rc=${?}
     fi
 fi

lib/pbench/server/database/database.py

@@ -1,8 +1,7 @@
 import sys
 
 from sqlalchemy import create_engine
-from sqlalchemy.ext.declarative import declarative_base
-from sqlalchemy.orm import scoped_session, sessionmaker
+from sqlalchemy.orm import declarative_base, scoped_session, sessionmaker
 
 from pbench.server import NoOptionError, NoSectionError
 

pytest.ini

@@ -2,3 +2,7 @@
 addopts = -s
 log_cli=False
 log_level=DEBUG
+filterwarnings=
+  # FIXME: drop this once `pytest-cov` is updated.
+  # Ref: https://github.com/pytest-dev/pytest-cov/issues/557
+  ignore:The --rsyncdir command line argument and rsyncdirs config variable are deprecated.:DeprecationWarning