List opened files in store on cleanup failure
List opened files in store on cleanup failure

This would let us know what is holding the store dir and why it cannot
be deleted

[#164301588]

Co-authored-by: Julia Nedialkova <7434cf6db6c17ad5b6ef614abe065a9cda1d30c1@hotmail.com>

cloudfoundry-incubator/guardian,cloudfoundry-incubator/guardian,cloudfoundry-incubator/guardian