qa: workunits: rest: test.sh: support outputting to custom files on expect

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
qa: workunits: rest: test.sh: helpers to get keys from xml/json files

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
qa: workunits: rest: test.sh: auth/add (fixup)

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
qa: workunits: rest: test.sh: multiple auth tests

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>