feat(v1.1): Implement /ping endpoint for v1.1

This patch creates a new endpoint /ping in v1.1 API, which is a
clone of the /health endpoint in v1.0. Because a new /health
endpoint will be added in v1.1 to return more detailed KPI of
Marconi server.

Implement blueprint: api-v1.1-ping-endpoint

Change-Id: I486c8a3583fc557c0b0578b0f73a6c6a2a3748b3
Replace basestring by six for python3 compatability

The builtin basestring abstract type was removed in python3,
use str instead, we need to using six.string_types to replace
the basestring for py3 compatibility.

Change-Id: Ie9fe7ef68d28902a384ba598c19f0cf3cd94d9bb
Replace unicode() by six.text_type for python3 compatability

Using six.text_type to replace the unicode() for py3
compatibility.

Change-Id: Ic90483fb014303a3703d45dc2293234ef24f96e9
Merge "Replace unicode() by six.text_type for python3 compatability"
Merge "Replace basestring by six for python3 compatability"