RFE: allow empty Ship date for a release

[pbabinca]

Curently I'm not able to set Ship date for a release:

usage: errata-tool release create [-h] --name NAME --product PRODUCT
                                  --product_version PRODUCT_VERSION --type
                                  TYPE --program_manager PROGRAM_MANAGER
                                  --blocker_flags BLOCKER_FLAGS
                                  --default_brew_tag DEFAULT_BREW_TAG

optional arguments:
  -h, --help            show this help message and exit
  --name NAME           eg. "rhceph-2.4"
  --product PRODUCT     eg. "RHCEPH"
  --product_version PRODUCT_VERSION
                        eg. "RHEL-7-CEPH-3"
  --type TYPE           eg. "QuarterlyUpdate"
  --program_manager PROGRAM_MANAGER
                        eg. "anharris"
  --blocker_flags BLOCKER_FLAGS
                        eg. "ceph-2.y"
  --default_brew_tag DEFAULT_BREW_TAG
                        eg. "ceph-3.0-rhel-7-candidate"

I see the code sets current date if not set: https://github.com/red-hat-storage/errata-tool/blob/master/errata_tool/release.py#L123

Errata Tool accepts releases with empty Ship date. In that case advisories are created with Ship date: ASAP. I'm wondering if it would be possible to set this with CLI as well.

[pbabinca]

I'm wondering if you would like to keep current functionality to set ship date to today?