BF: make Simple_Prep_docker run on OSX

[yarikoptic]

as @khinsen pointed out -- dockerfile preparation script doesn't work on OSX . This is a PR to address that

• no sed -i and readlink -f
• check if it works and fix the rest of OSX compatibility issues
• double check back on Linux systems that it works as expected

Closes #17
Relates to #15

[yarikoptic]

@satra -- I have no working docker on OSX, so could just verify that it seems to generate correct Dockerfile and then verify that it works on Linux. Could you give it a shot on OSX following current(modified) README.md

[satra]

will do - also added list of things to take care of today - #20.

[satra]

on osx:

$ ./Simple_Prep_docker Simple_Prep_docker-Dockerfile.in 
readlink: illegal option -- f
usage: readlink [-n] [file ...]

let me first update docker file before you make anymore changes.

[yarikoptic]

Are you sure you are in my branch? Check on invocation in readme - needs release and a date

[satra]

ah no. i was blindly using master.

[yarikoptic]

Needs a minor revert for cleanness

[yarikoptic]

Actually this change is not needed... I was blinded by the osx pain :-)

[yarikoptic]

pushed that little revert... @satra -- could you check if all is kosher on OSX so it could finally be merged/forgotten about? ;)

[satra]

works on my OSX version: 10.12.4 (16E195)