Previously, the behavior was to error out on the first invalid option
encountered. With this change, a best effort approach is made so that
all invalid options processed will be printed before exiting.

There is a caveat. The options are processed many times at varying
stages of server startup because the server is not aware of all valid
options immediately (e.g. plugins have to be loaded first before the
server knows what are the available plugin options). So, there are some
options that the server can determine are invalid "early" on, and there
are some options that the server cannot determine are invalid until
"later" on. For example, the server can determine an option such as
`--a` is an ambiguous option very early on but an option such as
`--this-does-not-match-any-option` cannot be labelled as invalid until
the server is aware of all available options.

Thus, it is possible that the server will still fail before printing out
all "invalid" options. You can see this by passing `--a
--obvious-invalid-option`.

Test cases were added to `mysqld_option_err.test` to validate that
multiple invalid options will be displayed in the error message.

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.