Fix exception of bind9 when /etc/bind/named.conf.options don't exist

Traceback (most recent call last):
  File "./sv2", line 11, in <module>
    load_entry_point('sv2==0.0.1', 'console_scripts', 'sv2')()
  File "/root/.local/lib64/python3.6/site-packages/sv2-0.0.1-py3.6.egg/sv2/command_line.py", line 4, in main
    sv2.main()
  File "/root/.local/lib64/python3.6/site-packages/sv2-0.0.1-py3.6.egg/sv2/main.py", line 170, in main
    run_checkers(checkers_modules, repots, checkers_options)
  File "/root/.local/lib64/python3.6/site-packages/sv2-0.0.1-py3.6.egg/sv2/main.py", line 124, in run_checkers
    c.run(r, opts[name])
  File "/root/.local/lib64/python3.6/site-packages/sv2-0.0.1-py3.6.egg/sv2_checkers/bind9.py", line 50, in run
    run_checkers(c, opts)
  File "/root/.local/lib64/python3.6/site-packages/sv2-0.0.1-py3.6.egg/sv2/helpers.py", line 41, in run_checkers
    getattr(c, m)()
  File "/root/.local/lib64/python3.6/site-packages/sv2-0.0.1-py3.6.egg/sv2_checkers/bind9.py", line 33, in check_allow
    with open("/etc/bind/named.conf.options", 'r') as f:
FileNotFoundError: [Errno 2] No such file or directory: '/etc/bind/named.conf.options'