[FEATURE REQUEST] Extend OpenVSwitch modules with VLAN and DB functions

[smarsching]

The OpenVSwitch modules do currently not provide functions for adding bridges that are children of an existing bridge and use a specific VLAN tag. They do not provide functions for setting arbitrary properties (e.g. setting a fixed MAC address for an interface) either.

Therefore the following changes are needed:

• Modify salt.states.openvswitch_bridge.present(…), adding two new optional parameters for the parent bridge and VLAN ID.
• Modify salt.modules.openvswitch.bridge_create(…), so that it takes two new optional parameters for the parent bridge and VLAN ID. This function is used by salt.states.openvswitch_bridge.present(…).
• Add a function bridge_to_parent(…) to salt.modules.openvswitch. This function is used to determine the parent of an existing bridge.
• Add a function bridge_to_vlan(…) to salt.modules.openvswitch. This function is used to determine the VLAN ID of an existing bridge.
• Add a module salt.states.openvswitch_db with a managed(…) function. This function can be used to make sure that a record in the OpenVSwitch database has certain values.
• Add a function db_get to salt.modules.openvswitch. This function is used to read a value from the OpenVSwitch database.
• Add a function db_set to salt.modules.openvswitch. This function is used to write a value to the OpenVSwitch database.

All these changes have been accepted into Salt before with PR #50564. However, this PR was made against the develop branch and they never got merged into master and thus never made it into a release.

I have now ported these changes to the current master and also made adjustments to make them fit the current guidelines (for example I added tests for all added or modified functions).

I will create a new PR with these changes soon. This issue has only been created to have an issue ID that can be referenced in the changelog entry.