[dashboard] Service steps data overflows cookie-based session storage

[Timur Sufiev]

Muranodashboard code doesn't explicitly clear session entries containing data of a service step, so when using cookie-based storage in case of intensive operations in UI it won't take long before storage is overflowed (4096 bytes limit) and some weird errors began to appear.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/123493

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/123493
Committed: https://git.openstack.org/cgit/stackforge/murano-dashboard/commit/?id=ea598d91abca3ac802d0f0c5bc1a8b937b1587af
Submitter: Jenkins
Branch: master

commit ea598d91abca3ac802d0f0c5bc1a8b937b1587af
Author: Timur Sufiev <email address hidden>
Date: Tue Sep 23 19:54:35 2014 +0400

    Cleanup leftover wizard data in session on adding App to Env

    Default horizon setting is to use cookie-based session storage, which
    has a limit of 4096 bytes (actually, a bit less), thus it can be
    overflown very quickly in case one user adds many applications.

    Closes-Bug: #1372963
    Change-Id: Icf5a908fa330c6a80f80c31bc59331735e3a86d4