Consider local project to be default for 'repo start'
Consider local project to be default for 'repo start'

The requirement to explicitly specify the local project when starting
a new repo branch is somewhat counter intuitive.

This patch uses the current directory's git tree as the default
project.

Tested by running

  'repo start <name>'

observed that the result is the same as if running

  'repo start <name> .'

Change-Id: If106caa801b4cd5ba70dbe8354a227d59f100aa3

TheQtCompany/git-repo,mer-tools/git-repo,lipro-yocto/git-repo,GerritCodeReview/git-repo,chzhong/git-repo,chzhong/git-repo,aosp-mirror/tools_repo,TheQtCompany/git-repo,nuclearmistake/repo,chenzilin/git-repo,couchbasedeps/git-repo,aosp-mirror/tools_repo,GerritCodeReview/git-repo,dodocat/git-repo,frogbywyplay/git-repo,gabbayo/git-repo,wavecomp/git-repo,11NJ/git-repo,nuclearmistake/repo,wavecomp/git-repo,lewixliu/git-repo,qioixiy/git-repo,lipro-yocto/git-repo,dodocat/git-repo,gabbayo/git-repo,qioixiy/git-repo,frogbywyplay/git-repo,couchbasedeps/git-repo,codetutil/git-repo,chenzilin/git-repo,mer-tools/git-repo,11NJ/git-repo,codetutil/git-repo,lewixliu/git-repo