Fix how SESSION_SECRET for paas-admin is generated
Fix how SESSION_SECRET for paas-admin is generated

We were generating the SESSION_SECRET env var for paas-admin wrong,
so it is always `session-(( grab ...`. This is because we use
spruce interpolation wrong

We fix it as the intention is use the UAA secret of the paas-admin
client.

To deploy this would logout all the users.

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf