This makes the start and stop scripts compatible with POSIX shells.

Overview of the changes:
- "function" statements removed, not necessary and incompatible
- dashes in function and variable names for lower ones (- to _)
- source statements changed for .
- double square brackets replaced for single ones
- double equal statements replaced for single ones
- &> (piping stdout and stderr to the same file) replaced for 2>&1 >
- sourcing of mycroft-skill-testrunner replaced with direct execution
with Bash
- replaced BASH_SOURCE with $0, these scripts are never sourced anyway
- replaced "echo -n" statements with "printf"
- merged the "" and "all" cases to a single one