ec2.api.Ec2InstanceWrapper.get_by_nametag: Remove LookupError from the docs.

It was removed in 9c4c2d4c8560d22341e84025faaa1e621921778c. See #11.
awsfabrictasks: No global imports.

Needed because the version is imported by setup.py.
HISTORY: About the backwards incompatible change introduced in #11.