Fix amulet tests that reference trusty_juno
Fix amulet tests that reference trusty_juno

Juno has been deprecated. A recent charm helper sysnc removed
references to trusty_juno. Therefore it is no longer defined.
Move checks back to icehouse.

Change-Id: I0272ad4f7a2339c6f60b4ba8a6ddfcb76cc3ded7

coreycb/charm-keystone,coreycb/charm-keystone