bridgescript: log script output at trace level
bridgescript: log script output at trace level

We currently log the bridge script only if there is an error. If there
is no error, we still capture the output, but at trace level. It is
useful to see the before/after configuration of routing and bridging
when debugging problems.

bac/juju,marcmolla/juju,ericsnowcurrently/juju,mikemccracken/juju,mjs/juju,marcmolla/juju,anastasiamac/juju,waigani/juju,bac/juju,mjs/juju,bac/juju,alesstimec/juju,alesstimec/juju,anastasiamac/juju,mjs/juju,marcmolla/juju,waigani/juju,bac/juju,ericsnowcurrently/juju,ericsnowcurrently/juju,ericsnowcurrently/juju,mikemccracken/juju,anastasiamac/juju,anastasiamac/juju,anastasiamac/juju,mjs/juju,alesstimec/juju,alesstimec/juju,mikemccracken/juju,ericsnowcurrently/juju,mjs/juju,mikemccracken/juju,marcmolla/juju,bac/juju,marcmolla/juju,waigani/juju,waigani/juju,mikemccracken/juju,mjs/juju,mjs/juju,alesstimec/juju