Comment 2 for bug 1760956

The following confirms and details the current state of the two options, which are essentially at odds with one-another in terms of declaring dependencies in a sane way.

ie. When using a venv, we should never include system packages.

#### All src (reactive) OpenStack charms:
ubuntu@beisner-bastion:~/git/release-tools⟫ find -type f -name layer.yaml | sort
./aodh/src/layer.yaml
./barbican-softhsm/src/layer.yaml
./barbican/src/layer.yaml
./ceph-fs/src/layer.yaml
./designate-bind/src/layer.yaml
./designate/src/layer.yaml
./gnocchi/src/layer.yaml
./keystone-ldap/src/layer.yaml
./manila-generic/src/layer.yaml
./manila/src/layer.yaml
./neutron-api-odl/src/layer.yaml
./openvswitch-odl/src/layer.yaml
./tempest/src/layer.yaml

#### Those which take a stance on use_venv and/or include_system_packages:
ubuntu@beisner-bastion:~/git/release-tools⟫ find -type f -name layer.yaml | sort | xargs egrep "system|venv"
./aodh/src/layer.yaml: use_venv: True
./aodh/src/layer.yaml: include_system_packages: True
./barbican-softhsm/src/layer.yaml: use_venv: true
./barbican-softhsm/src/layer.yaml: include_system_packages: true
./barbican/src/layer.yaml: use_venv: true
./barbican/src/layer.yaml: include_system_packages: true
./designate/src/layer.yaml: use_venv: True
./designate/src/layer.yaml: include_system_packages: True
./gnocchi/src/layer.yaml: use_venv: True
./gnocchi/src/layer.yaml: include_system_packages: True
./keystone-ldap/src/layer.yaml: use_venv: True
./keystone-ldap/src/layer.yaml: include_system_packages: True
./manila/src/layer.yaml: use_venv: true
./manila/src/layer.yaml: include_system_packages: true
./neutron-api-odl/src/layer.yaml: use_venv: True
./neutron-api-odl/src/layer.yaml: include_system_packages: True
./openvswitch-odl/src/layer.yaml: use_venv: True
./openvswitch-odl/src/layer.yaml: include_system_packages: True

#### Those which do not declare either, leaving it up to version chance:
ceph-fs
designate-bind
manila-generic
tempest