Harmonize execution services and execution result

[vinjana]

The SSHExecutionService and LocalExecutionService use inconsistent behaviour with respect to

• dealing with stdout and stderr (once its part of resultLines, once not)
• dealing with wrapping commands in Bash

ExecutionResults should be able to handle stdout and stderr separately (but maybe optionally also intermingled, which is useful to keep the relative timing of output in both streams). Proper intermingled dealing, however, will still keep the lines from each separated!

Consider also whether asynchronous execution really makes sense, if much of the code is synchronous.

[vinjana]

We now only use the LocalExecutionService. Inconsistent behaviour, therefore, does not warrant the effort to harmonize this.