Mac support

[madmatah]

Bug Report

As reported in #675 , the Quick start instructions fail on Mac because of the following problems :

While executing make cluster:

• readlink does not support the -f option on Mac
• uuidgen returns uppercase strings on Mac

Also, the documentation recommends to tune sysctl value tune vm/max_map_count for Elasticsearch, but it fails on mac.

Possible Solution

• Find a POSIX alternative for readlink -f and apply it in bin/arnold and bin/init-cluster (hint here?)
• Fix the uuidgen case issue
• Update the documentation to mention that the sysctl command needs special care on mac (possible solution here)

[aarajbhattarai]

While executing bin/arnold -c eugene -e development -a hello bootstrap:

• hostname -I does not work on Mac. (https://ss64.com/osx/hostname.html)

[aarajbhattarai]

@jmaupetit
Which Operating system do you use for arnold?

[jmaupetit]

Which Operating system do you use for arnold?

GNU/Linux.