sync: Add option '--force-remove-dirty'
sync: Add option '--force-remove-dirty'

Forcefully remove dirty projects if option '--force-remove-dirty' is given.
The '--force-remove-dirty' option can be used to remove previously used
projects with uncommitted changes. WARNING: This may cause data to be lost
since uncommitted changes may be removed with projects that no longer exist
in the manifest.

Change-Id: I844a6e943ded522fdc7b1b942c0a1269768054bc

codetutil/git-repo,gabbayo/git-repo,mer-tools/git-repo,TheQtCompany/git-repo,TheQtCompany/git-repo,gabbayo/git-repo,GerritCodeReview/git-repo,couchbasedeps/git-repo,aosp-mirror/tools_repo,mer-tools/git-repo,lipro-yocto/git-repo,lewixliu/git-repo,couchbasedeps/git-repo,aosp-mirror/tools_repo,codetutil/git-repo,lipro-yocto/git-repo,lewixliu/git-repo,GerritCodeReview/git-repo