Get ambari mirror with curl instead of wget

That was implemented in 0.2 but wasn't 'backported' back to 0.3.
The rationale is that unlike 'curl', 'wget' is not installed by
default on CentOS

Change-Id: I16c920dcb0b496fd229754c49ba7ed9fe19ad1e8
Merge "Get ambari mirror with curl instead of wget"