install the leap-keyring package, after the leap apt source has been added and apt has been refreshed

Change-Id: I485420c4ea50f8c3f6699b9b8073dc6c67b7a353
Merge branch 'bug/leap_keyring_2492' into develop

Change-Id: Idda4e0301b3e349581fef36989706a487b05ecd8