Use system CA certificate file

When SSL is being used and the --ca-file option is
not specified use an available system CA file to
verify the server's certificate.

Change-Id: Id5c9fda6fd9bd05cde3c2a9160a6e72cef086a44

glanceclient/common/http.py

@@ -16,6 +16,7 @@
 import copy
 import httplib
 import logging
+import os
 import socket
 import StringIO
 import urlparse
@@ -201,7 +202,10 @@ class VerifiedHTTPSConnection(httplib.HTTPSConnection):
                                          cert_file=cert_file)
         self.key_file = key_file
         self.cert_file = cert_file
-        self.ca_file = ca_file
+        if ca_file is not None:
+            self.ca_file = ca_file
+        else:
+            self.ca_file = self.get_system_ca_file()
         self.timeout = timeout
         self.insecure = insecure
 
@@ -233,6 +237,20 @@ class VerifiedHTTPSConnection(httplib.HTTPSConnection):
 
         self.sock = ssl.wrap_socket(sock, **kwargs)
 
+    @staticmethod
+    def get_system_ca_file():
+        """"Return path to system default CA file"""
+        # Standard CA file locations for Debian/Ubuntu, RedHat/Fedora,
+        # Suse, FreeBSD/OpenBSD
+        ca_path = ['/etc/ssl/certs/ca-certificates.crt',
+                   '/etc/pki/tls/certs/ca-bundle.crt',
+                   '/etc/ssl/ca-bundle.pem',
+                   '/etc/ssl/cert.pem']
+        for ca in ca_path:
+            if os.path.exists(ca):
+                return ca
+        return None
+
 
 class ResponseBodyIterator(object):
     """A class that acts as an iterator over an HTTP response."""

glanceclient/shell.py

@@ -73,8 +73,9 @@ class OpenStackImagesShell(object):
                  'not necessary if your key is prepended to your cert file.')
 
         parser.add_argument('--ca-file',
-            help='Path of CA SSL certificate(s) used to sign the remote '
+            help='Path of CA SSL certificate(s) used to verify the remote '
-                 'server\'s certificate.')
+                 'server\'s certificate. Without this option glance looks '
+                 'for the default system CA certificates.')
 
         parser.add_argument('--timeout',
             default=600,