girder-client --certificate option doesn't work with --api-url
This comes from the following check in `cli.py`:

```python
    if certificate and ctx.obj.scheme != 'https':
        raise click.BadArgumentUsage(
            'A URI scheme of "https" is required for option "--certificate"')
```

Most of the time we don't pass the scheme, we use `--api-url` instead.
diff --git a/clients/python/girder_client/cli.py b/clients/python/girder_client/cli.py
index 7a2a501f7..49b5b872e 100755
--- a/clients/python/girder_client/cli.py
+++ b/clients/python/girder_client/cli.py
@@ -159,8 +159,8 @@ _CONTEXT_SETTINGS = dict(help_option_names=['-h', '--help'])
               show_default=True,
               cls=_AdvancedOption
               )
-@click.option('--certificate', default=None,
-              help='Specify path to SSL certificate',
+@click.option('--ca-certificate', default=None,
+              help='Specify path to CA certificate to use to verify the server',
               show_default=True,
               cls=_AdvancedOption
               )
@@ -175,7 +175,7 @@ _CONTEXT_SETTINGS = dict(help_option_names=['-h', '--help'])
 @click.pass_context
 def main(ctx, username, password,
          api_key, api_url, scheme, host, port, api_root,
-         no_ssl_verify, certificate, token, retries, verbose):
+         no_ssl_verify, ca_certificate, token, retries, verbose):
     """Perform common Girder CLI operations.
 
     The CLI is particularly suited to upload (or download) large, nested
@@ -200,13 +200,13 @@ def main(ctx, username, password,
             raise click.BadArgumentUsage(
                 'Option "--api-url" and option "--%s" are mutually exclusive.' %
                 name.replace('_', '-'))
-    if certificate and no_ssl_verify:
+    if ca_certificate and no_ssl_verify:
         raise click.BadArgumentUsage(
-            'Option "--no-ssl-verify" and option "--certificate" are mutually exclusive.')
+            'Option "--no-ssl-verify" and option "--ca-certificate" are mutually exclusive.')
 
     ssl_verify = True
-    if certificate:
-        ssl_verify = certificate
+    if ca_certificate:
+        ssl_verify = ca_certificate
     if no_ssl_verify:
         ssl_verify = False
 
@@ -215,10 +215,6 @@ def main(ctx, username, password,
         scheme=scheme, apiUrl=api_url, apiKey=api_key, sslVerify=ssl_verify, token=token,
         retries=retries)
 
-    if certificate and ctx.obj.scheme != 'https':
-        raise click.BadArgumentUsage(
-            'A URI scheme of "https" is required for option "--certificate"')
-
 
 def _set_logging_level(verbosity):
     if not verbosity:
['clients/python/girder_client/cli.py']