sysrepoctl: use a separate repository subdirectory for submodules
sysrepoctl: use a separate repository subdirectory for submodules

to avoid libyang warnings about parsing submodules, keep submodules
in a separate subdirectory to keep sysrepoctl aware what is module and
what is submodule. Since it is subdirectory of the modules' location,
libyang is able to find them automatically.

morganzhh/sysrepo,morganzhh/sysrepo,morganzhh/sysrepo,morganzhh/sysrepo,morganzhh/sysrepo,morganzhh/sysrepo,morganzhh/sysrepo