kiji-schema-shell: DDLSHELL-73. cleanup resource leak in integration test

issue: https://jira.kiji.org/browse/DDLSHELL-73
review: https://review.kiji.org/r/1865
commit: https://github.com/kijiproject/kiji-schema-shell/commit/0c79ef173ab44316de385def3aa29bdb56643552