[FIXED JENKINS-30502] trim job name upon rename

If a job is renamed to a string with trailing whitespace, exceptions are
thrown as the application attempts to rename the job directory in the
file system, and the job can be neither deleted nor renamed again
through the UI. This problem occurs only when renaming a job, and not
when initially creating a job, because job names are trimmed when first
created.  This change trims the job name for rename operations as well,
so that the name-setting behavior is consistent across create/update
operations and inadvertent leading/trailing whitespace is removed before
it can cause problems.