testscript: improve ssh() network diagnosis and logging

We will be able to better understand if a network issue is caused by
the VM host or the VM.

Now, in ssh() we also check if the network is still reachable or
if someone broke on the host.

A possible missing IP in VM host error might be reported like this:

```
The VM host is not in the same network as IP 192.168.5.2! Networks:
[IPv4Network('192.168.1.0/24'), IPv4Network('192.168.2.0/24'), IPv4Network('192.168.3.0/24'), IPv4Network('192.168.4.0/24'), IPv4Network('192.168.100.0/24')]
```

On-behalf-of: SAP philipp.schuster@sap.com
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

Author: phip1611

tests/testscript.py

@@ -2018,17 +2018,35 @@ def ssh(machine: Machine, cmd, user="root", password="root", ip="192.168.1.2"):
     """
     Runs the specified command in the Cloud Hypervisor VM via SSH.
 
-    The specified machine is used as SSH jump host.
+    The SSH connection will be established from the specified machine.
 
-    :param machine: Machine to run SSH on
+    Performs some sanity network checks beforehand:
+    - does the IP actually share a (local) network with the given machine?
+    - is the IP ping-able?
+
+    :param machine: Machine to execute the SSH command on.
     :param cmd: The command to execute via SSH
     :param user: user for SSH login
     :param password: password for SSH login
     :param ip: SSH host to log into
     :return: status and output
     """
+
+    # Sometimes we experienced test runs where the host lost IPs. We therefore
+    # check that early and always for better debuggability.
+    assert_ip_in_local_192_168_net24(machine, ip)
+
+    if not is_pingable(machine, ip, 1, 1):
+        raise RuntimeError(f"VM with IP {ip} is not pingable")
+
+    # And here we check if the guest also responds via SSH.
     status, out = machine.execute(
-        f"sshpass -p {password} ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no {user}@{ip} {cmd}"
+        f"sshpass -p {password} "
+        + "ssh "
+        + "-o UserKnownHostsFile=/dev/null "
+        + "-o StrictHostKeyChecking=no "
+        + "-o ConnectTimeout=1 "
+        + f"{user}@{ip} {cmd}"
     )
     return status, out