SERVER-15557 warn if we detect configurations for multiple storage engines

This re-applies commit cf1c4bb5a9da98ec831ff0a30ae78abe81e1d1b0 with the following modifications:
    a bug fix for when mongod is run without any command line options
    converts the multiple config error to a warning.
    removed storage_options.js (added in original commit but not needed anymore)
Merge remote-tracking branch 'upstream/master'