[JENKINS-65327] File parameters no longer overwrite previous files #11989

This is a regression in 2.278, it worked in 2.277.

Steps to reproduce:

	
Create a freestyle job
	
Define a file parameter
	
Trigger a build, uploading a file
	
Trigger another build, uploading a file



Expected behavior: The file is replaced, the build is successful (2.277 and earlier)

Actual result: The build fails with:

Building in workspace /var/jenkins_home/workspace/fs
Copying file to f
FATAL: Destination '/var/jenkins_home/workspace/fs/f' already exists
org.apache.commons.io.FileExistsException: Destination '/var/jenkins_home/workspace/fs/f' already exists
	at org.apache.commons.io.FileUtils.moveFile(FileUtils.java:2266)
	at org.apache.commons.fileupload.disk.DiskFileItem.write(DiskFileItem.java:405)
	at hudson.FilePath.copyFrom(FilePath.java:1092)
	at hudson.model.FileParameterValue$2.setUp(FileParameterValue.java:173)
	at hudson.model.Build$BuildExecution.doRun(Build.java:157)
	at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:513)
	at hudson.model.Run.execute(Run.java:1907)
	at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
	at hudson.model.ResourceController.execute(ResourceController.java:97)
	at hudson.model.Executor.run(Executor.java:429)
Finished: FAILURE