Test connection using ping

Rework `DataSourceDefinition.prototype.testConnection` to invoke `ping` method in the workspace app.

Improve error handling in `invokeMethodInWorkspace` to catch common errors and translate them to a useful error in the master process.

Mark `DataSourceDefinition.testConnection` as deprecated, implement it using the original `testConnection` code running in the master process.

See also https://github.com/strongloop/strong-studio/issues/109

/to @ritch please review