Use random password generator for IsolatedCreds

Currently, for IsolatedCreds provider, new tenant/user will be created for
testing. However, the user password is hardcoded(with 'pass' as the
default) in the implementation. This patch change that to use random
password generator for user creation.

Change-Id: I36d64e6313a5b4edc03acad64bcdaeab680f9ce0
Implements: blueprint random-password-for-user-creation
diff --git a/requirements.txt b/requirements.txt
index 60dee97..fefd019 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -21,5 +21,5 @@
 iso8601>=0.1.9
 fixtures>=0.3.14
 testscenarios>=0.4
-tempest-lib>=0.5.0
+tempest-lib>=0.6.1
 PyYAML>=3.1.0