Increase the storage from 30GB to 50GB

When running some jobs, it failed due to no enough space [1]

[1]: https://ci.trustedfirmware.org/blue/organizations/jenkins/mbed-tls-pr-head/detail/PR-5608-head/1/pipeline/395

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: I5afa4079b210e5ab59e4bc25bad5e8640f9cd68c
1 file changed
tree: 3f2525ddcfea20239261f1f250600d18bba8cd2b
  1. packer_config.json
  2. ubuntu.sh