Add version field to tryjob metadata.
Add version field to tryjob metadata.

Will make it easier to change the format of the metadata without
breaking compatibility with older cbuildbot versions.

BUG=None
TEST=Submitted job to test server.

Change-Id: Id69af64e3135538da2c1b3da170ea0d8e3e38ca6
Reviewed-on: https://gerrit.chromium.org/gerrit/18314
Tested-by: Ryan Cui <5ce1592d53754a87a44fc2eb7b63d5f77cf50fdb@chromium.org>
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

coreos/chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,coreos/chromite,zhang0137/chromite,chadversary/chromiumos.chromite,zhang0137/chromite,coreos/chromite