CI: Initial commit for moving CI into source repo

Create tests/CI directory and add files used by Jenkins to
build and test Asterisk.

With this commit, Jenkins will run the Asterisk Unit Tests using
the Jenkinsfile at tests/CI/unittests.jenkinsfile.  Bash scripts
to do the actual building and testing are also in the same directory.
Output is placed in tests/CI/output so that directory has been
added to .gitignore.

Change-Id: I9448065465e6de2b878634510ace8fd1ef378608