processutils.execute() does not allow setting environment variables

[Roman Prykhodchenko]

Setting environment variables is essential for various kind of tasks. The most recent one that is required by the Ironic project is setting the LANG variable to be able to rely to the process output.

subprocess.Popen supports passing environment variables so this is quite easy to do.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/86021

[Openstack Gerrit (openstack-gerrit)]

Reviewed: https://review.openstack.org/86021
Committed: https://git.openstack.org/cgit/openstack/oslo-incubator/commit/?id=51778f9eef2dd88a949679f0280f69ee99fd5567
Submitter: Jenkins
Branch: master

commit 51778f9eef2dd88a949679f0280f69ee99fd5567
Author: Roman Prykhodchenko <email address hidden>
Date: Tue Apr 8 14:37:44 2014 +0300

    Allow passing environment variables to execute()

    Some of the projects might need to pass environment variables
    to the processes they launch. For instance, if something needs
    to rely on the process' output it should be able to pass LANG="C"
    in order to set the correct localization.

    This patch adds a env_variables parameter to processutils.execute()
    which allows to pass news variables or replace the value of the existing
    ones for the process.

    Closes-bug: #1304284
    Change-Id: If801e11391bf7cf66518533443c3b29af53653e5