jujud version fetched with combined output for bootstrap tools

[Michael Foord]

I tweaked the logging in golxc to emit some logging at Warning level instead of Trace. This caused bootstrap to fail as the jujud command run to fetch the version number causes golxc logging to be emitted on standard error - and combined output is fetched to get the version number. Only standard out should be used instead!

Incidentally, using jujud to get the version number should not be calling lxc commands! (On startup jujud will determine if the system supports lxc containers, it looks like this is happening a bit early.)

The failure error I saw was:

 ERROR failed to bootstrap environment: cannot upload bootstrap tools: invalid version "2015-05-06 22:20:30 WARNING golxc.run.lxc-config golxc.go:448 run: lxc-config [lxc.lxcpath]\n2015-05-06 22:20:30 WARNING golxc.run.lxc-config golxc.go:448 run: lxc-config [lxc.lxcpath]\n1.23.3.1-trusty-amd64" printed by jujud