openstack.check: Be more careful when claiming credentials are invalid

In order to check the user's credentials at the start of deployment, we
try to run `glance image-list`. I found a situation where this command
failed despite my credentials being correct. Morph outputted a
misleading error message that said 'Wrong OpenStack credentials'

The code now checks that the error returned by 'glance' does indeed
look like a credentials error. If it doesn't, the full error output is
displayed. The error I encountered now gets a message like this:

    ERROR: openstack.check failed with code 1: ERROR: Failed to connect
    to OpenStack instance at https://example.com:5000/v2.0:
    [('SSL routines', 'SSL3_GET_SERVER_CERTIFICATE', 'certificate verify
    failed')]

(If you are curious, I fixed this by running `update-ca-certificates`.)

1 files changed, 11 insertions, 4 deletions

diff --git a/openstack.check b/openstack.check
index edc37cc1..a6856c31 100755
--- a/openstack.check
+++ b/openstack.check
@@ -77,9 +77,16 @@ class OpenStackCheckExtension(morphlib.writeexts.WriteExtension):
                    '--os-password', password,
                    '--os-auth-url', auth_url,
                    'image-list']
-        try:
-            cliapp.runcmd(cmdline)
-        except cliapp.AppException:
-            raise cliapp.AppException('Wrong OpenStack credentals.')
+
+        exit, out, err = cliapp.runcmd_unchecked(cmdline)
+
+        if exit != 0:
+            if err.startswith('The request you have made requires ' \
+                              'authentication. (HTTP 401)'):
+                raise cliapp.AppException('Invalid OpenStack credentials.')
+            else:
+                raise cliapp.AppException(
+                    'Failed to connect to OpenStack instance at %s: %s' %
+                    (auth_url, err))
 
 OpenStackCheckExtension().run()