Ignore ElephantSQL in system tests

Currently, the ElephantSQL team is preventing normal create/delete
behavior for service instances.  This causes the system test to fail
while testing against ElephantSQL.  This change ignores the
ElephantSQL tests until a resolution can be found.

[#72156172]
Merge 72156172-remove-elephantsql to master

[Completes #72156172]