logging: always log process arguments and stderr when at debug

Also remove ad-hoc logging of this information.

src/ocrmypdf/exec/__init__.py

@@ -77,12 +77,21 @@ def run(args, *, env=None, **kwargs):
             if new_args0:
                 args[0] = new_args0
 
-    log.debug(args)
+    process_log = log.getChild(os.path.basename(program))
+    process_log.debug("Running: %s", args)
     if sys.version_info < (3, 7) and os.name == 'nt':
         # Can't use close_fds=True on Windows with Python 3.6 or older
         # https://bugs.python.org/issue19575, etc.
         kwargs['close_fds'] = False
-    return subprocess_run(args, env=env, **kwargs)
+    proc = subprocess_run(args, env=env, **kwargs)
+    if process_log.isEnabledFor(logging.DEBUG):
+        try:
+            stderr = proc.stderr.decode('utf-8', 'replace')
+        except AttributeError:
+            stderr = proc.stderr
+        if stderr:
+            process_log.debug("stderr = %s", stderr)
+    return proc
 
 
 def get_version(program, *, version_arg='--version', regex=r'(\d+(\.\d+)*)', env=None):

src/ocrmypdf/exec/ghostscript.py

@@ -311,7 +311,6 @@ def generate_pdfa(
         ]
     )
     args_gs.extend(fspath(s) for s in pdf_pages)  # Stringify Path objs
-    log.debug(args_gs)
     try:
         with Path(output_file).open('wb') as output:
             p = run(args_gs, stdout=output, stderr=PIPE, check=True)
@@ -342,5 +341,3 @@ def generate_pdfa(
                 "Ghostscript had to remove PDF 'overprinting' from the "
                 "input file to complete PDF/A conversion. "
             )
-        else:
-            log.debug(stderr)

src/ocrmypdf/exec/tesseract.py

@@ -282,7 +282,6 @@ def generate_hocr(
     # to the number of order parameters here
     args_tesseract.extend([input_file, prefix, 'hocr', 'txt'] + tessconfig)
     try:
-        log.debug(args_tesseract)
         p = run(
             args_tesseract,
             stdout=PIPE,
@@ -381,7 +380,6 @@ def generate_pdf(
 
     args_tesseract.extend([input_image, prefix, 'pdf', 'txt'] + tessconfig)
     try:
-        log.debug(args_tesseract)
         p = run(
             args_tesseract,
             stdout=PIPE,