update-rc: Fix usage for various cases

Fixes:
 * fail fast in case of trouble
 * treat 1.0 as special working branch and be ok to remove it
 * select origin/1.0 as source of the local 1.0 branch

Thank to this it can be used in clean repository.
10 jobs for 1.0 in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.SlapRunner.ResilienceTest-Master

00:23:36

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:22:57

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

07:36:39

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

06:26:52

passed SlapOS.SlapRunner.ResilienceTest-Master

00:26:11

passed SlapOS.SlapRunner.ResilienceTest-Master

00:23:10

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:30:26

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:27:31

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:21:19

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

07:27:39