[core] restructure to allow PIP packaging

OK - so I have to admit I *hate* the fact that PIP seems to require a
subdirectory named like the library.

But since the PIP package is something really nifty to have (thanks to
@tony again!!!), I updated the codebase to hopefully conform with what
PIP expects. Testruns so far look promising...

bumblebee_status/util/cli.py

@@ -0,0 +1,44 @@
+import os
+import shlex
+import subprocess
+import logging
+
+
+def execute(cmd, wait=True, ignore_errors=False, include_stderr=False, env=None):
+    """Executes a commandline utility and returns its output
+
+    :param cmd: the command (as string) to execute, returns the program's output
+    :param wait: set to True to wait for command completion, False to return immediately, defaults to True
+    :param ignore_errors: set to True to return a string when an exception is thrown, otherwise might throw, defaults to False
+    :param include_stderr: set to True to include stderr output in the return value, defaults to False
+    :param env: provide a dict here to specify a custom execution environment, defaults to None
+
+    :raises RuntimeError: the command either didn't exist or didn't exit cleanly, and ignore_errors was set to False
+
+    :return: output of cmd, or stderr, if ignore_errors is True and the command failed
+    :rtype: string
+    """
+    args = shlex.split(cmd)
+    logging.debug(cmd)
+    try:
+        proc = subprocess.Popen(
+            args,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT if include_stderr else subprocess.PIPE,
+            env=env,
+        )
+    except FileNotFoundError as e:
+        raise RuntimeError("{} not found".format(cmd))
+
+    if wait:
+        out, _ = proc.communicate()
+        if proc.returncode != 0:
+            err = "{} exited with code {}".format(cmd, proc.returncode)
+            if ignore_errors:
+                return err
+            raise RuntimeError(err)
+        return out.decode("utf-8")
+    return ""
+
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4