add a --trace-python option
add a --trace-python option

This can help debug issues by tracing all the repo python code with
the standard trace module.

Change-Id: Ibb7f4496ab6c7f9e130238ddf3a07c831952697a
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/234833
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@google.com>
Reviewed-by: David Pursehouse <e7b5c6a4a3dbaca972851f8c075e19915752593f@collab.net>

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