Handle case for no local DNS more properly

This exception has been observed on a system where DNS is configured strangely. The fallback as this change directs to makes it work fine.

Issue

$ (main) everest run config.yml
Waiting for server ...
Failed to start Everest with error:
Traceback (most recent call last):
  File "/home/berland/projects/everest/everest/detached/jobs/everserver.py", line 242, in main
    cert_path, key_path, key_pw = _generate_certificate(config)
  File "/home/berland/projects/everest/everest/detached/jobs/everserver.py", line 368, in _generate_certificate
    cert_name = get_machine_name()
  File "/home/berland/projects/everest/everest/detached/jobs/everserver.py", line 54, in get_machine_name
    for ptr_record in resolver.resolve(reverse_name, "PTR")
  File "/home/berland/venv/jun24/lib/python3.10/site-packages/dns/resolver.py", line 1565, in resolve
    return get_default_resolver().resolve(
  File "/home/berland/venv/jun24/lib/python3.10/site-packages/dns/resolver.py", line 1529, in get_default_resolver
    reset_default_resolver()
  File "/home/berland/venv/jun24/lib/python3.10/site-packages/dns/resolver.py", line 1542, in reset_default_resolver
    default_resolver = Resolver()
  File "/home/berland/venv/jun24/lib/python3.10/site-packages/dns/resolver.py", line 944, in __init__
    self.read_resolv_conf(filename)
  File "/home/berland/venv/jun24/lib/python3.10/site-packages/dns/resolver.py", line 1038, in read_resolv_conf
    raise NoResolverConfiguration("no nameservers")
dns.resolver.NoResolverConfiguration: no nameservers

where reverse_name=<DNS name 20.1.168.192.in-addr.arpa.>

Approach Catch and fallback.

equinor / everest

Handle case for no local DNS more properly #37