Fix bare except clauses in shutils.py, __main__.py, and utils.py

[koteshyelamati]

Fix bare except: clauses that catch BaseException (including SystemExit, KeyboardInterrupt, and GeneratorExit), replacing them with except Exception: or more specific exception types.

Changes:

pox/shutils.py (lines 49, 79, 302):

• get_home(): except: → except Exception:
• get_username(): except: → except Exception:
• Path traversal loop: except: → except Exception:

pox/__main__.py (lines 35, 49, 53):

• Main try block: except: → except Exception:
• sys.argv access: except: → except IndexError: (more specific — only IndexError is possible here)
• exec() call: except: → except Exception:

pox/utils.py (line 168):

• File conversion: except: → except Exception:

Bare except: clauses are considered bad practice (PEP 8 / flake8 E722) because they silently swallow signals like KeyboardInterrupt, making programs impossible to interrupt with Ctrl+C.