[cli] environment-create-session command print session id in stdout

[Anastasia Kuznetsova]

During cli automatisation I figured out that 'environment-create-session' command prints session id to the console, just like usual string.
Need to make output of this command similar to other command.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/235496

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/235496
Committed: https://git.openstack.org/cgit/openstack/python-muranoclient/commit/?id=aaef2fca3f5ceacb951a66d3136dc28fd1b5f81d
Submitter: Jenkins
Branch: master

commit aaef2fca3f5ceacb951a66d3136dc28fd1b5f81d
Author: Anastasia Kuznetsova <email address hidden>
Date: Thu Oct 15 20:00:07 2015 +0300

    Use standard formatters for environment-create-session output

    This commit adds usage of standard formatters for environment-create-session
    command's output instead of just 'printing' session id to the stdout
    without any ability to parse it for example during automatisation of
    CLI testing.

    Closes-Bug: #1506560
    Change-Id: I19bce3c2fe662002f4c5a24f9637514bce9ee39f