Make symmetric_secret optional in ccng template

This is no longer a required property in ccng.
Moreover, its absence is used to indicate that the
UAA is using an asymmetric signature for tokens so
it has to be optional in the yaml template.
Merge pull request #59 from tekul/feature/ccngsecret

Make symmetric_secret optional in ccng template
Bump dea

dea shortlog 2ca4fcd..e7db702
Jesse Zhang (1):
      Remove broad rescue [#46751287]

Maria Shaldibina and Max Brunsfeld (3):
      Reorganize buildpack fixtures
      Compute reserved memory and disk correctly in ResourceManager
      Support memory and disk overcommit factors [#46311945]
Merge git://github.com/cloudfoundry/cf-release