Fix OpenStack coverage tool
Fix OpenStack coverage tool

Can no longer rely on Zuul's layout.yml to just have str's in its
set of test names, so we coerce to str.  Somewhat hacky workaround
but works for now.

Change-Id: Ib6676f0f106345e6919e81b1ca5327c8f2e5e8dd

chair6/bandit,pombredanne/bandit,pombredanne/bandit,stackforge/bandit,stackforge/bandit