Fix to use proper random values

In several tests, they need int values but use rand_name().
Especially, test_security_group_rules.py has a potentially bug.
And, when we will change the rand_name() to return string value, the
errors will occur in others.
So this commit fixes it and belows:
 * just import the module instead of importing the function
 * minor comment typo

Change-Id: Ic957c741b9ad3631d726dc6cfb5ecb9e0077a884
Merge "Fix to use proper random values"