This commit adds a Devstack MURANO_APPS variable which can be used to
install directly from the Git murano-apps repository (repository and
branch customizable) some Murano packages.
E.g MURANO_APPS="io.murano.apps.apache.Tomcat,io.murano.apps.Guacamole"
The murano-apps repository is cloned only if at least one application
is defined in MURANO_APPS.
Implements: blueprint import-apps-devstack
Change-Id: I57f959ddafd62cc726d4f5f80fec27bc86bf05d1
6843856c3d