Serialize layer env

[splhack]

Fix #547

• Layer env can be set from JSON, but it doesn't propagate. Serialize it into XML.
• Fix layer get_env.

[larsbijl]

Hi @splhack,

Thank you for your contribution!

When I submit a layer with an env variable set, it gets the following traceback:

cuebot_1  | com.imageworks.spcue.SpecBuilderException: Failed to parse job spec XML, org.jdom.input.JDOMParseException: Error on line 1: Attribute value "b'HELLO'" of type NMTOKEN must be a name token.

Here is the example I used to test with

#!/usr/bin/env python
from outline import Outline
from outline.cuerun import OutlineLauncher
from outline.modules.shell import Shell

ol = Outline(name='testing', name_unique=True)
layer1 = Shell('layer1', command=['sleep 5'], range='1-10', threads=1, threadable=True)
layer1.set_env('HELLO', 'WORLD')
ol.add_layer(layer1)

launcher = OutlineLauncher(ol)
jobs = launcher.launch(False)
print(jobs)

[splhack]

@larsbijl thank you for testing!
I found out Python2 future.types.newstr.newstr issue on XML via only set_env (JSON is fine.)
Added a workaround, and verified with unittests.

[larsbijl]

Thanks @splhack! tested and works great.