vcs.rb doesn't detect git submodules as vcs
Mostly a followup of #12239 as this was already about a similar use case.
When I run make-snapshot with a srcdir as target thats inside a submodule it doesn't detect it as vcs.
My command line and the output:
~/dev/sailfish/jolla/pkgs/mer_core/ruby/ruby/:./tool/make-snapshot -srcdir=../$PWD snapshot'
Traceback (most recent call last):
1: from ./tool/make-snapshot:584:in
detect': does not seem to be under a vcs: ..//home/bidar/dev/sailfish/jolla/pkgs/mer_core/ruby/ruby (VCS::NotFoundError)