Use psycopg2's string handling to escape password string

This allows the password to contain single quotes and should make it safe to
use randomly generated passwords (provided passwords can be represented in the
connection encoding).

library/postgresql_user

@@ -142,8 +142,10 @@ def user_exists(cursor, user):
 
 def user_add(cursor, user, password, role_attr_flags):
     """Create a new database user (role)."""
-    query = "CREATE USER \"%(user)s\" with PASSWORD '%(password)s' %(role_attr_flags)s"
-    cursor.execute(query % {"user": user, "password": password, "role_attr_flags": role_attr_flags})
+    query = 'CREATE USER "%(user)s" WITH PASSWORD %%(password)s %(role_attr_flags)s' % {
+        "user": user, "role_attr_flags": role_attr_flags
+    }
+    cursor.execute(query, {"password": password})
     return True
 
 def user_alter(cursor, user, password, role_attr_flags):
@@ -168,8 +170,10 @@ def user_alter(cursor, user, password, role_attr_flags):
 
         if password is not None:
             # Update the role attributes, including password.
-            alter = "ALTER USER \"%(user)s\" WITH PASSWORD '%(password)s' %(role_attr_flags)s"
-            cursor.execute(alter % {"user": user, "password": password, "role_attr_flags": role_attr_flags})
+            alter = 'ALTER USER "%(user)s" WITH PASSWORD %%(password)s %(role_attr_flags)s' % {
+                "user": user, "role_attr_flags": role_attr_flags
+            }
+            cursor.execute(alter, {"password": password})
         else:
             # Update the role attributes, excluding password.
             alter = "ALTER USER \"%(user)s\" WITH %(role_attr_flags)s"