xci: Introduce XCI_LOOP variable to control what to do properly

xci: Introduce XCI_LOOP variable to control what to do properly

XCI has different jobs/loops to run
- patchset verification jobs (currently bifrost and osa in future)
- periodic jobs (bifrost and osa)
- daily jobs (for OPNFV platform deployment and testing)

The same scripts/playbooks used by XCI will also be used by developers.

We need to do different things depending on the context the scripts
and playbooks are executed.
- periodic jobs will use latest of everything to find working versions
of the components. (periodic osa will use unpinned role requirements
for example)
- daily jobs will use pinned versions in order to bring up the platform
and run OPNFV testing against it. (daily deployment will use pinned
versions and role requirements for example)
- developers might choose to use pinned versions or latest

Depending on what loop we are running, we need to do things differently
in scripts and playbooks. This variable will help us to do this in easy way.

We can of course do pattern matching of the job name but it will not
work if the scripts are used outside of Jenkins.

The default loop for non-Jenkins execution is set to daily as we want
developers to use working versions unless they change it to something
else intentionally.

Change-Id: Iff69c77ae3d9db2c14de1783ce098da9e9f0c83d
Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>