RFR: Parse .ssh/config in git-pr if needed

[Erik Duveblad via github.com]

Hi all,

`git-pr` needs to find the `URI` for a remote and that can be a bit tricky if an SSH "alias" (set up in `~/.ssh/config`) is involved. This patch adds a little `ssh` module with a `SSHConfig` class that can parse most fields out of an `ssh_config` file (most crucially the `Hostname` field). This way `git-pr` can be a little smarter about figure out the hostname of the forge.

## Testing
- [x] `sh gradlew test` passes
- [x] Added an additional unit test

Thanks,
Erik

----------------

Commits:
 - af597194:	Remove tabs
 - c03bd2f7:	Remove stray debug printing
 - 1ef6a56a:	Parse .ssh/config in git-pr if needed

Pull request:
https://git.openjdk.java.net/skara/pull/88

Webrev:
https://webrevs.openjdk.java.net/skara/88/webrev.00

Patch:
https://git.openjdk.java.net/skara/pull/88.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/88/head:pull/88