Fixed random test in SchemaBackendTestCase: testRemoveAttributeTypeReferencedByNameForm() always failed when run after testRemoveObjectClassReferencedByNameForm() which does not properly cleanup schema changes.

SchemaBackendTestCase.java:
In testRemoveAttributeTypeReferencedByNameForm() and testRemoveObjectClassReferencedByNameForm(), properly reset schema state after test run.
When submitting changes for ldapmodify, always use stdin (instead of temporary files).
Consolidated all runModify*() and args*() methods.
Code cleanup.

TestCaseUtils.java:
Use try-with-resources.