internal: master conn check for get space utils

Added validation of the connection to the `utils.get_space`
method before receiving the space through the connection.

Closes #331

Author: GRISHNOV

crud/common/utils.lua

@@ -97,6 +97,12 @@ end
 
 function utils.get_space(space_name, replicasets)
     local replicaset = select(2, next(replicasets))
+
+    if replicaset.master.conn.error ~= nil then
+        local error_msg = string.format('The connection to the master is not valid: %s',
+                                         replicaset.master.conn.error)
+        error(error_msg)
+    end
     local space = replicaset.master.conn.space[space_name]
 
     return space