[ISSUE #2067] Add logs when collecting disk space usage

[imaffe]

What is the purpose of the change

1. issue logics disk maybe full soon, so reclaim space, -1.0 #2067 , need more detailed log to find why the path is invalid.

Brief changelog

1. added 3 log statement

Verifying this change

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[coveralls]

Coverage increased (+0.07%) to 50.92% when pulling c3e2958 on imaffe:affe-0623-#2067-addlogs-disk-usage into e923a35 on apache:master.