Implements a "maintenance mode" for PVC clusters. For now, the only
thing this mode does is disable node fencing while the state is true.
This allows the administrator to tell PVC that network connectivity,
etc. might be interrupted and to avoid fencing nodes.
Closes#70
Move all API calls to a new common function called call_api to
facilitate easier future changes. Use this function to implement API key
handling via request header value as well as integrate the request URI
generation and debug output handling.
Closes#65
Joshua Boniface