server does not fail if invalid cert is specified for grpc transport

[edaniszewski]

By "invalid", I mean the cert does not exist. This is because the cert is not checked for presence and is instead just passed right to the client constructor. This happens in a block where we trap errors and instead of failing, let them pass through so we can try again later. The intent being that if we fail to connect, it doesn't terminate the server.

It looks like two things could happen here:

• a preliminary check on startup to verify that the configured file does in fact exist
• more granular exception handling on plugin client creation so we do not fall through when this file not found error is raised

timestamp='2020-04-09T19:04:02.803746Z' logger='synse_server.plugin' level='warning' event='failed to register configured plugin - will attempt re-registering later' address='emulator-plugin:5001' protocol='tcp' error=FileNotFoundError(2, 'No such file or directory')