Fix : sort variables fetched from env list

In bionic, when exporting env variables, the env list displays
variables in unsorted format.
While fetching we are getting 'https_proxy' before 'http_proxy'
which is failing in comparison to our expected values[1].
This patch sorts the variables fetched from env.

[1] http://logs.openstack.org/30/643130/3/check/devstack-unit-tests/effbf7a/job-output.txt.gz#_2019-03-13_23_12_35_465026

Change-Id: Ie504eabf0d3fec1b97bc711e2702c06bcf75d158
1 file changed