sanity: add a comment to ensure CONNECTIVITY_CHECK_URIS is correct

In sanity.bbclass, in function check_connectivity :
Connectivity is tested by fetching URIs in variable CONNECTIVITY_CHECK_URIS.
If none is accessible, the status error is ambiguous.

It says to ensure the host's network is correctly configured but
never if the remote is available.

Signed-off-by: Shubham Kulkarni <skulkarni@mvista.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes-global/sanity.bbclass

@@ -357,6 +357,7 @@ def check_connectivity(d):
             if len(msg) == 0:
                 msg = "%s.\n" % err
                 msg += "    Please ensure your host's network is configured correctly.\n"
+                msg += "    Please ensure CONNECTIVITY_CHECK_URIS is correct and specified URIs are available.\n"
                 msg += "    If your ISP or network is blocking the above URL,\n"
                 msg += "    try with another domain name, for example by setting:\n"
                 msg += "    CONNECTIVITY_CHECK_URIS = \"https://www.example.com/\""