Allow non-word characters in vs_bridge external_ids

Currently, the type enforces a regex for vs_bridge
external id values that is way to strict. Essentially
that entries are \w*=\w*.

Bridge external ids commonly include non-word characters
, like '-' (ie: br-ex).

This patch updates the parameter checking to allow
any non-whitespace characters.

Change-Id: I26d47b9744e6e294b0b1bc09cd6268f5587f8bd8