Added end2end tests for invalid manifests.

Not complete yet, but adds a few basic ones.
Added E2E prefix to end2end test names.

Includes more tests for invalid manifest parsing in E2E.
Updated test manifest names to be descriptive.

Insead of (in)valid[N].manifest, the names are now
descriptor.manifest, which makes the files themselves more
self-documenting.
Moved reader tests out of a directory.