RFR: Really fix so tests ignore .gitconfig

[Magnus Ihse Bursie]

It turned out that [SKARA-913](https://bugs.openjdk.java.net/browse/SKARA-913) which fixed unwanted side effects of [SKARA-868](https://bugs.openjdk.java.net/browse/SKARA-868), in fact broke Skara testing completely the way SKARA-868 was supposed to fix. In SKARA-913 only a few of the Skara tests were properly configured to really ignore the local configuration; something I discovered lately when running all tests on a machine with a .gitconfig that foils several git tests from running.

Since there is no really single point of entry to say to the Repository logic "I am now running a test", I have created a wrapper TestableRepository.init(), which calls Repository.init() and makes sure ignoreConfiguration is on.

At least this solves the problem for me. There might be other tests hiding where other strange configurations provoke a failure; I know of no systematic way to find all these, so I'll guess we have to fix that when it is discovered.

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Commit messages:
 - Replace Repository with TestableRepository in tests.

Changes: https://git.openjdk.java.net/skara/pull/1066/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1066&range=00
  Stats: 285 lines in 22 files changed: 53 ins; 3 del; 229 mod
  Patch: https://git.openjdk.java.net/skara/pull/1066.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1066/head:pull/1066

PR: https://git.openjdk.java.net/skara/pull/1066