Add basic command line utility

It doesn't so much other than print version, but it's set up and in
place for adding commands in the next commits.

pbrx/cmd/main.py

@@ -0,0 +1,98 @@
+# Copyright 2018 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import argparse
+import json
+import logging
+import logging.config
+import os
+import sys
+
+try:
+    import yaml
+except ImportError:
+    yaml = None
+
+import pbr.version
+
+log = logging.getLogger("pbrx")
+
+
+def _read_logging_config_file(filename):
+    if not os.path.exists(filename):
+        raise ValueError("Unable to read logging config file at %s", filename)
+
+    ext = os.path.splitext(filename)[1]
+    if ext in (".yml", ".yaml"):
+        if not yaml:
+            raise ValueError(
+                "PyYAML not installed but a yaml logging config was provided."
+                " Install PyYAML, or convert the config to JSON."
+            )
+
+            return yaml.safe_load(open(filename, "r"))
+
+    elif ext == ".json":
+        return json.load(open(filename, "r"))
+
+    return filename
+
+
+def setup_logging(log_config, debug):
+    if log_config:
+        config = _read_logging_config_file(log_config)
+        if isinstance(config, dict):
+            logging.config.dictConfig(config)
+        else:
+            logging.config.fileConfig(config)
+    else:
+        log.addHandler(logging.StreamHandler())
+        log.setLevel(logging.DEBUG if debug else logging.INFO)
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="pbrx: Utilities for projects using pbr"
+    )
+    parser.add_argument(
+        "--version",
+        action="version",
+        version=str(pbr.version.VersionInfo("pbrx")),
+    )
+    parser.add_argument(
+        "--debug", help="Emit debug output", action="store_true"
+    )
+    parser.add_argument(
+        "--log-config",
+        help="Path to a logging config file. Takes precedence over --debug",
+    )
+
+    subparsers = parser.add_subparsers(
+        title="commands", description="valid commands", help="additional help"
+    )
+
+    args = parser.parse_args()
+    setup_logging(args.log_config, args.debug)
+    try:
+        return args.func(args)
+
+    except Exception as e:
+        log.exception(str(e))
+        return 1
+
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

setup.cfg

@@ -18,6 +18,10 @@ classifier =
     Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
 
+[entry_points]
+console_scripts =
+    pbrx = pbrx.cmd.main:main
+
 [build_sphinx]
 all-files = 1
 warning-is-error = 1