Merge tag 'sparks-3.7' into develop

3.7
harden the remote platform/uname detection against shell stderr output.
do not include the email subject prefix unless stated otherwise in django settings (else 1flow tests break now that we have a custom subject prefix for admins)
preliminary work for remote-to-remote fabric task execution.
Don't try to switch the virtualenv if SPARKS_JENKINS exists and is set to anything.
bump version in __init__.py
Merge branch 'release/3.7.1'