bump runtime-schema

[delivers #79618158]

Submodule src/github.com/cloudfoundry-incubator/runtime-schema cab51b0..34a4ec2:
  > DesireLRP acts as an upsert
  > lrp watchers test should properly test updates
  > nuke lrp identifier magic from orbit

Signed-off-by: Eric Malm <emalm@pivotal.io>
Create final release 0.555 for build 309