Fixed main.partition_open_files_limit, innodb.innodb_bug12400341 failures.

These testcases use --max-connections=N command line option, which
was declared PARSE_EARLY during the merge. Embedded didn't handle
early options and failed to start due to unknown command line
option.

libmysqld/lib_sql.cc:
  Let embedded handle early options.
sql/mysqld.cc:
  Moved handling of early options to a separate function.
sql/mysqld.h:
  Moved handling of early options to a separate function.