Metadata repository sometimes retunes HTTP 500

[Timur Nurlygayanov]

When issuing lots of requests (e.g. clicking "create service" button in the UI) sometimes Metadata Repository returns HTTP 500 error, having the following in the log:
{noformat}
2013-11-19 17:09:46.466 98955 DEBUG root [-] Asserting there is just one archive in cache folder. Clear folder /var/folders/v_/tx6yj_4s10j_j3d6plp3755c0000gn/T/murano-cache/ui in case of Assertion Error get_existing_hash /Users/ativelkov/dev/murano/murano-repository/muranorepository/utils/archiver.py:133
2013-11-19 17:09:46.467 98955 ERROR muranorepository.main [-] Exception on /v1/client/ui [GET]
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main Traceback (most recent call last):
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main File "/Users/ativelkov/dev/murano/murano-repository/.venv/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main response = self.full_dispatch_request()
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main File "/Users/ativelkov/dev/murano/murano-repository/.venv/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main rv = self.handle_user_exception(e)
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main File "/Users/ativelkov/dev/murano/murano-repository/.venv/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main reraise(exc_type, exc_value, tb)
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main File "/Users/ativelkov/dev/murano/murano-repository/.venv/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main rv = self.dispatch_request()
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main File "/Users/ativelkov/dev/murano/murano-repository/.venv/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main return self.view_functions[rule.endpoint](**req.view_args)
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main File "/Users/ativelkov/dev/murano/murano-repository/muranorepository/api/v1.py", line 37, in get_archive_data
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main request.args.get('hash'))
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main File "/Users/ativelkov/dev/murano/murano-repository/muranorepository/api/utils.py", line 37, in get_archive
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main existing_hash = archive_manager.get_existing_hash(cache_dir)
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main File "/Users/ativelkov/dev/murano/murano-repository/muranorepository/utils/archiver.py", line 134, in get_existing_hash
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main assert len(existing_caches) < 2
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main AssertionError
2013-11-19 17:09:46.467 98955 TRACE muranorepository.main
{noformat}

[Timur Sufiev (tsufiev-x)]

Fix introduced in https://review.openstack.org/#/c/57415/