Support Phantomas per metrics from syscall

Attempt n.2: Support Phantomas per metrics from syscall

In order to properly run get_fact_definitions, make a "dummy" call to phantomas bin against a SimpleHTTPServer to get a list of supported metrics, which depend on the installed version of Phantomas. In case of failure, use a list of metrics defined in phantomas_info.py. Please read the line notes bellow.