force logs as json

[prune998]

Drone server is logging JSON by default.
This PR force the drone-runner-docker to log as JSON too.

[CLAassistant]

All committers have signed the CLA.

[tphoney]

Hey @prune998 thanks for the PR 🍺 !,
However this may have unforeseen implications of changing the output format, as people maybe relying on its current format. This is something that makes sense, would you change your PR to make this optional, so that it can be enabled by the end user if they choose.

[prune998]

I'll look into this asap.

[prune998]

@tphoney I just added a bool flag to switch to json logs.
Please, review.

Thanks.

[bradrydzewski]

The exec command is used to manually run build locally from an interactive terminate which is why we have text logging as opposed to json logging. Not sure we want json logging here. But it makes sense for the daemon.

[bradrydzewski]

I suggest backing out the changes to this file. The exec command is used for local development and testing only and we would never need / use json logging here.