Fix the auto instrumentation command

Fixes open-telemetry#566

Author: ocelotl

docs/examples/auto-instrumentation/README.md

@@ -92,7 +92,7 @@ Span(name="serv_request", context=SpanContext(trace_id=0x9c0e0ce8f7b7dbb51d1d6e7
 Now, kill the execution of `server_instrumented.py` with `ctrl + c` and run this instead:
 
 ```sh
-$ opentelemetry-auto-instrumentation opentelemetry-python/opentelemetry-auto-instrumentation/example/server_uninstrumented.py
+$ opentelemetry-auto-instrumentation python opentelemetry-python/opentelemetry-auto-instrumentation/example/server_uninstrumented.py
 ```
 
 In the console where you previously executed `client.py`, run again this again:

opentelemetry-auto-instrumentation/src/opentelemetry/auto_instrumentation/auto_instrumentation.py

@@ -15,22 +15,22 @@
 # limitations under the License.
 
 from logging import getLogger
-from runpy import run_path
+from os import environ, execl
+from os.path import abspath, dirname, pathsep
+from shutil import which
 from sys import argv
 
-from pkg_resources import iter_entry_points
-
 logger = getLogger(__file__)
 
 
 def run() -> None:
 
-    for entry_point in iter_entry_points("opentelemetry_instrumentor"):
-        try:
-            entry_point.load()().instrument()  # type: ignore
-            logger.debug("Instrumented %s", entry_point.name)
+    python_path = environ.get("PYTHONPATH", "")
+    filedir_path = dirname(abspath(__file__))
+
+    if filedir_path not in python_path:
+        environ["PYTHONPATH"] = pathsep.join([filedir_path, python_path])
 
-        except Exception:  # pylint: disable=broad-except
-            logger.exception("Instrumenting of %s failed", entry_point.name)
+    executable = which(argv[1])
 
-    run_path(argv[1], run_name="__main__")  # type: ignore
+    execl(executable, executable, *argv[2:])

opentelemetry-auto-instrumentation/src/opentelemetry/auto_instrumentation/sitecustomize.py

@@ -0,0 +1,28 @@
+# Copyright The OpenTelemetry Authors
+#
+# 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.
+
+from logging import getLogger
+
+from pkg_resources import iter_entry_points
+
+logger = getLogger(__file__)
+
+
+for entry_point in iter_entry_points("opentelemetry_instrumentor"):
+    try:
+        entry_point.load()().instrument()  # type: ignore
+        logger.debug("Instrumented %s", entry_point.name)
+
+    except Exception:  # pylint: disable=broad-except
+        logger.exception("Instrumenting of %s failed", entry_point.name)