Exception class Bad_AVU_Value should inherit ValueError directly

[d-w-moore]

• irods.message.Bad_AVU_Value should be descended from ValueError for irods.test.meta_test.TestMeta.test_add_obj_meta_empty to pass.

Originally posted by @d-w-moore in #531 (comment)

[alanking]

Is this effort to fix a failing test, or a refactor / enhancement?

[d-w-moore]

Yes. Pretty much that, a fix of a failing test. But it does fit : Bad_AVU_Value should or at least can be considered a type of ValueError..

[d-w-moore]

#588 will include the fix for this.

[alanking]

Addressed by changes in #588.