Removes 'positive' tag from tests.

Also removes brackets where tag is a single value. This should be
finally cleanup the tags, see the following:

$ grep -r "@attr" tempest | cut -d: -f2 | sort -u
    @attr(type='gate')
    @attr(type=['negative', 'gate'])
    @attr(type='smoke')
$

Change-Id: I243800c597996c0dbcf153d66946062df6d298ab
Implements: blueprint set-gate-attribute
diff --git a/tempest/api/compute/servers/test_multiple_create.py b/tempest/api/compute/servers/test_multiple_create.py
index a705dd3..63bb86d 100644
--- a/tempest/api/compute/servers/test_multiple_create.py
+++ b/tempest/api/compute/servers/test_multiple_create.py
@@ -60,7 +60,7 @@
 
         return resp, body
 
-    @attr(type=['positive', 'gate'])
+    @attr(type='gate')
     def test_multiple_create(self):
         resp, body = self._create_multiple_servers(wait_until='ACTIVE',
                                                    min_count=1,
@@ -103,7 +103,7 @@
                           min_count=min_count,
                           max_count=max_count)
 
-    @attr(type=['positive', 'gate'])
+    @attr(type='gate')
     def test_multiple_create_with_reservation_return(self):
         resp, body = self._create_multiple_servers(wait_until='ACTIVE',
                                                    min_count=1,