[JENKINS-58779] LogRotator stops, if build was deleted externally (#4138)

* [JENKINS-58779] LogRotator stops cleaning, if build was deleted externally

The deletion of a build/run in Jenkins is handled by the delete() method.

It throws an exception, when the build directory on disk has already been
removed and stops deleting the build.

Unfortunately, the hudson.tasks.LogRotator.perform(Job<?, ?>) method does
not check for this exception and will STOP cleaning up, once even just one
build throws that exception.

This behaviour is fixed in the following ways in this change:

1.) The Run.delete() method must still unlink the job, even if the build
    directory has been removed externally.

2.) The log output of Run.delete() must be made less verbose (it prints the
    ENTIRE folder content by default, into the job that is doing the cleanup)

3.) The LogRotator.perform() method must handle the exceptions being thrown
    by delete() gracefully.

Signed-off-by: Martin H Schroeder <martin.h.schroeder@intel.com>

* Small change to copyright header (removed blank line)

n/t

Signed-off-by: Martin H Schroeder <martin.h.schroeder@intel.com>

* Incorporated changes proposed by Oleg Nenashev

 - Usage of Util.fileToPath
 - Addition of @since headers to public API methods

Signed-off-by: Martin H Schroeder <martin.h.schroeder@intel.com>

* Added fixes for comments raised by Oleg Nenashev and Jeff Thompson

This adds a collective IOException raised for all sub-exceptions
encountered during the cleanup process.

Signed-off-by: Martin H Schroeder <martin.h.schroeder@intel.com>