When passing in an invalid value (e.g. incorrect data type) for a variable, the
server startup will fail with misleading error messages.

The behavior **before** this change:

For server options:
- The error message will indicate that the argument is being adjusted to a valid value
- Server startup still fails

For plugin options:
- The error message will indicate that the argument is being adjusted to a valid value
- The plugin is still disabled
- Server startup fails with a message that it does not recognize the plugin option

The behavior **after** this change:

For server options:
- Output that an invalid argument was provided
- Exit server startup

For plugin options:
- Output that an invalid argument was provided
- Disable the plugin
- Attempt to continue server startup

All new code of the whole pull request, including one or several files that are
either new files or modified ones, are contributed under the BSD-new license. I
am contributing on behalf of my employer Amazon Web Services, Inc.