Add scanlib for producing keyboard scancodes

Add scanlib, a library for turning characters into keyboard scancodes
which are needed for scripted keyboard input to VirtualBox VMs.

The keyboard scancode strings returned by this library consist of groups
of two or four hex bytes: two for a key pressed and released, four if a
modifier key such as shift is involved.

The char2scancode function is complemented by two functions for special
keys, esc2scancode and enter2scancode.

Partial-Bug: 1312764
Implements: blueprint openstack-training-labs
Change-Id: Id8691fff1499cc2428e4b7858c908c117f3c4bce
Merge "Add scanlib for producing keyboard scancodes"