User omnisharp.json take precedence over flags we set on command line

[henryju]

If the user has a ~/.omnisharp/omnisharp.json in his home directory (for example if he is using VSCode), then it will override the flags we pass on the command line. This can lead to unexpected behavior.

A solution could be to pass our flags using the highest priority mechanism:

An omnisharp.json file located in the working directory which OmniSharp has been pointed at

See https://github.com/OmniSharp/omnisharp-roslyn/wiki/Configuration-Options