Test fetch and clone with credentials

Places repository URL, private key, and user name information outside
the repository so that the test private keys and repository URLs do not
need to be shared in the public repository.  That allows testing with
real repositories (like github and bitbucket) and real private keys
(like mine).

Uses a parameterized test which generates test parameters
by reading from ~/.ssh/auth-data/repos.csv.  In addition
to the repos.csv file contents, the test always uses the
https://github.com/jenkinsci/git-client-plugin.git repository for a test.

JGit version of this test does not exist yet.