package_manager: fix linter issues

The rename of methods makes linter thing these are new issues:

- Ignore the f"" warning, as f-string is not optimal for this use-case.
- Use RuntimeError instead of the generic Exception.  It is still too
  generic and mock prints stack trace if it happens, but
  package_manager.py probably deserves it's own exception (#1477).

mock/py/mockbuild/package_manager.py

@@ -34,7 +34,7 @@ def _package_manager_from_string(name):
         return Dnf
     if name == 'microdnf':
         return MicroDnf
-    raise Exception('Unrecognized package manager "{}"'.format(name))
+    raise RuntimeError(f'Unrecognized package manager "{name}"')
 
 
 def _package_manager_exists(pm_class, config_opts, chroot=None):
@@ -84,6 +84,7 @@ def _package_manager_class_fallback(config_opts, buildroot, fallback):
                 return pm_class
 
             if not bootstrap:
+                # pylint: disable=consider-using-f-string
                 print("""WARNING! WARNING! WARNING!
 You are building package for distribution which uses {0}. However your system
 does not support {0}. You can continue with {1}, which will likely succeed,
@@ -97,7 +98,7 @@ def _package_manager_class_fallback(config_opts, buildroot, fallback):
 
             return pm_class
 
-    raise Exception(f"No package from {fallbacks[desired]} found, desired {desired}")
+    raise RuntimeError(f"No package from {fallbacks[desired]} found, desired {desired}")
 
 
 def package_manager(buildroot, bootstrap_buildroot, fallback):