Fix qemu login prompt recognition

Most of the times we boot a new VM, login message shows '#' symbol
at the end. However, we are using '# ' (with space) to indicate
availability the user prompt. This can lead to an unrecognised
login prompt if message contain any color after the symbol.

With this patch, we take '#' symbol only into account, so we are able to
cover as much as cases as possible by default.

libkirk/qemu.py

@@ -143,7 +143,7 @@ def setup(self, **kwargs: dict) -> None:
         self._tmpdir = kwargs.get("tmpdir", None)
         self._user = kwargs.get("user", None)
         self._password = kwargs.get("password", None)
-        self._prompt = kwargs.get("prompt", "# ")
+        self._prompt = kwargs.get("prompt", "#")
         self._image = kwargs.get("image", None)
         self._initrd = kwargs.get("initrd", None)
         self._kernel = kwargs.get("kernel", None)