Patch: Add 'slavename' to available platform matching properties

[abierbaum@…]

I find that I often want to match a build platform against a specific buildslave host. With the current options this wasn't available. Instead you had to match family, os, etc against what you knew the build slave supported. This is nice when you don't know what buildslaves are available, but is a bit of a pain sometimes.

This patch adds 'slavename' to the list of properties that are used in the platform selection matching rules.

[cmlenz]

Implemented in [510], although I went with the name “name” instead of “slavename” to be consistent with the brevity of the others ;)

Thanks!