Add function to check host network connectivity

[cynepco3hahue]

covers #29

[lukas-bednar]

@cynepco3hahue It is great, just please add dummy test which pings 127.0.0.1.

regarding to ping6, I am not sure whether it will work, because in Host.init there is ipv4 validation for Host.ip, so it basically impossible to create instance of ipv6 Host. Also I can find that function on other places ...

rrmngmnt/host.py:62:        if not netaddr.valid_ipv4(ip):
rrmngmnt/network.py:201:                if netaddr.valid_ipv4(default_gw[0]):
rrmngmnt/network.py:221:                if netaddr.valid_ipv4(ip[0]):
rrmngmnt/network.py:272:            if netaddr.valid_ipv4(interface_ip):
tests/test_common.py:9:    assert netaddr.valid_ipv4(ip)

Please open issue to support ipv6 hosts.

[lukas-bednar]

I think this param is not necessary, you can use netaddr.valid_ipv6(self.host.ip) function to decide what command to use. like:

ping_cmd = "ping6" if netaddr.valid_ipv6(self.host.ip) else "ping"

[lukas-bednar]

not all instances supports sudo ... use apt addon instead ...

addons:
  apt:
    packages:
    - iputils-ping