patchp4: respect init.defaultBranch

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> In `git p4 clone`, we hard-code the branch name `master` instead of
> looking what the _actual_ initial branch name is. Let's fix that.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---

>     p4: respect init.defaultBranch
>     
>     Just something I noticed while working on the big master -> main rename
>     in the test suite.
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-782%2Fdscho%2Fgit-p4-and-init.defaultBranch-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-782/dscho/git-p4-and-init.defaultBranch-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/782
>
>  git-p4.py | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/git-p4.py b/git-p4.py
> index 4433ca53de..52ddb1d7b2 100755
> --- a/git-p4.py
> +++ b/git-p4.py
> @@ -4186,7 +4186,7 @@ def run(self, args):
>  
>          # create a master branch and check out a work tree
>          if gitBranchExists(self.branch):
> -            system([ "git", "branch", "master", self.branch ])
> +            system([ "git", "branch", currentGitBranch(), self.branch ])
>              if not self.cloneBare:
>                  system([ "git", "checkout", "-f" ])
>          else:
>
> base-commit: 7f7ebe054af6d831b999d6c2241b9227c4e4e08d