agentwrapper: try labgrid-python3 for agent environment

Allow probing of a labgrid-python3 executable and use that if available.
This allows the setup of a distinct python environment with the
necessary modules for agent operation. Since this is probed
automatically raise a debug message in case labgrid-python3 is not found
to aid in debugging.

Signed-off-by: Rouven Czerwinski <rouven.czerwinski@linaro.org>

Author: Emantor

labgrid/util/agentwrapper.py

@@ -60,20 +60,30 @@ def __init__(self, host=None):
                 ['rsync', '-e', ' '.join(ssh_opts), '-tq', agent,
                  f'{host}:{agent_remote}'],
             )
+            agent_python = "labgrid-python3" if subprocess.call(ssh_opgs + [host, '--', 'which', 'labgrid-python3']) else "python3"
+            if agent_python == "python3":
+                self.logger.debug(
+                    f"labgrid-python3 on {host} not found, using python3 which requires system installed python modules for agents"
+                )
             self.agent = subprocess.Popen(
-                ssh_opts + [host, '--', 'python3', agent_remote],
+                ssh_opts + [host, '--', agent_python, agent_remote],
                 stdin=subprocess.PIPE,
                 stdout=subprocess.PIPE,
                 start_new_session=True,
             )
         else:
             # run locally
             self.fdpass, remote_fdpass = socket.socketpair()
+            agent_python = "labgrid-python3" if which("labgrid-python3") else "python3"
+            if agent_python == "python3":
+                self.logger.debug(
+                    "labgrid-python3 not found locally, using python3 which requires system installed python modules for agents"
+                )
             with remote_fdpass:
                 env = os.environ.copy()
                 env["LG_FDPASS"] = str(remote_fdpass.fileno())
                 self.agent = subprocess.Popen(
-                    ['python3', agent],
+                    ['agent-python', agent],
                     stdin=subprocess.PIPE,
                     stdout=subprocess.PIPE,
                     env=env,