Adding updateOnly flag to loadUpdateData for cases where we want to *only* update existing records.  This allows the use of the tag in a way that only columns we need will be updated and prevents failures if a record is unexpectly absent from the target database. (Due to insufficient fields in the input file.)
Merge branch 'contrib/add_update_only_flag_to_loadupdatedata' of https://github.com/kellerj/liquibase into kellerj-contrib/add_update_only_flag_to_loadupdatedata
CORE-2062 Add onlyUpdate flag to loadUpdateData

Changed flag from updateOnly to onlyUpdate
Merge branch 'kellerj-contrib/add_update_only_flag_to_loadupdatedata'