Provides a system to determine available interfaces in a range

[abates]

This request adds a method to slice lists of interfaces in order to facilitate provisioning. Sometimes upstream connections are placed within a given range of interfaces. For instance, a primary connection may always go in the range of Ethernet[1-24] and a secondary connection may go into Ethernet[25-48]. If a switch has all the interfaces Ethernet[1-48] available, then the two needed slices are returned. If a subset of needed interfaces are available, then only those interfaces in the subset are returned. For instance:

slice_interface_range(["Ethernet2", "Ethernet3", "Ethernet4", "Ethernet6", "Ethernet7", "Ethernet8"], "Ethernet1", "Ethernet5")

will effectively produce:

["Ethernet2", "Ethernet3", "Ethernet4"], ["Ethernet6", "Ethernet7", "Ethernet8"]