Only using 'id' OR 'name' from pb path in datastore.Entity.save.

This was introduced in #289 and discovered while rebasing those
changes into #281.

The datastore backend fails if both 'id' and 'name' are set on
a key, so this only copies the parts of the saved pb key that
are actually set.
Merge pull request #291 from dhermes/fix-key-error-in-entity-save

Only using 'id' OR 'name' from pb path in datastore.Entity.save.
Test adding encrypted key.
Test commit to determine if regression is run.
Re-encrypt to make sure file correct.
Putting back original regression test.
Squashed commit of PR #281 in main repo.
Removing most of Travis for test branch.
Removing uses of tox to try to speed up BUILD.
Small tweak to ditch tox and install library on Travis.

See previous commit for context:
5277854a79b8dbce76062ac7dc7945a76b6dd679
Make pep8 ignore the pb auto-generated file.

See previous two for context:
823976f37ea95165e92b7254d5ef2e897896831b
5277854a79b8dbce76062ac7dc7945a76b6dd679
Helping Travis import Google protobuf.

See previous for context:
1036c852ac1f21fbb3625c24739f36d6a3ede285
823976f37ea95165e92b7254d5ef2e897896831b
5277854a79b8dbce76062ac7dc7945a76b6dd679