Description of problem:
spacewalk-repo-sync  fails in case both options --sync-kickstart and --url are specified.

Version-Release number of selected component (if applicable):
spacewalk-utils-2.0.2-13

How reproducible:
100%

Steps to Reproduce:
1.Create Custom Software channel. 
2.Create Yum repository that comprises Kickstart Tree.

Actual results:
# spacewalk-repo-sync -c custom-channel --sync-kickstart --url http://test.redhat.com/repo/
Repo URL: http://testredhat.com/repo/
Packages in repo:                 1
Packages already synced:          0
Packages to sync:                 1
1/1 : test-regular-Test_RPM_305-0.1-1-0.x86_64
Linking packages to channel.
Repo http://ibm-x3690x5-01.rhts.eng.bos.redhat.com/repo/ has 0 errata.
ERROR: null value in column "label" violates not-null constraint

Sync completed.
Total time: 0:00:00

Expected results:
If the same repository is set up via WebUI and assigned to the channel the kickstart tree is synchronized correctly.

The option --sync-kickstart should be ignored for repositories set from CLI via option [-u|--url] as they can not be identified.