Added check for xenstore key existance before checking value

Change-Id: I12c5d094272747cbb0c8bcc40e43db1c0008d8eb
Re-added user_config value to the Compute fixture

Change-Id: I29e0219d6f4c67578070afea8c26a12755606547
Merge "Added check for xenstore key existance before checking value"
Merge "Re-added user_config value to the Compute fixture"