Cadvisor object url protocol not validated correctly

[cgmcintyr]

Initialising a Cadvisor object without a protocol can result in errors when making requests to paths joined onto url.

For example:

from cadvisor import Cadvisor

cad = Cadvisor('127.0.0.1:8080', '1.3')

Results in that Cadvisor instance's 'get' methods trying to urljoin a string onto 127.0.0.1:8080.

For example calling cad.get_machine_info():

pycadvisor/cadvisor/cadvisor.py

Lines 39 to 41 in d15c00a

	def get_machine_info(self):
	data = self.__get_json_data(api.machine_info_url(self.api_url))
	return MachineInfo(data)

In this instance would result in callling api.machine_info_url with base_url arg set to 127.0.0.1:8080

pycadvisor/cadvisor/api.py

Lines 13 to 14 in d15c00a

	def machine_info_url(base_url):
	return urljoin(base_url, 'machine')

Which would return the string 'machine/', which leads to a MissingSchema: Invalid URL 'machine' when this string is passed as argument into self.__get_json_data.

[cgmcintyr]

First step would be to create a test case. After this look at adding http:// to start of url cadvisor is being initialised with if there is no procotol given.