Support multiple keys for key rotation

[mingyech]

Let the station be able to use multiple private keys so that the key can be rotated over time. Updated components:

• Detector: try multiple private keys while checking decoy registration in TLS client hello packets
• Application:
  • separate the ZMQ private key apart from the application private key
  • try multiple keys while authenticating with the client in prefix transport

Updated config directory structure:

$ tree /var/lib/conjure/
/var/lib/conjure/
├── app_config.toml
├── ClientConf
├── conjure.conf
├── conjure_regtrack.conf
├── phantom_subnets.toml
├── privkey
│   ├── privkey1
│   └── privkey2
├── reg_config.toml
├── regtrack_config.toml
└── zmq_privkey

Also fixes an issue with pfring interface name in the detector startup script, and issues with rust tests linking with libtapdance.