oc adm migrate fails with "Forbidden: signature annotations cannot be set".

Issue

• When we run oc adm migrate storage, we get following error.

# oc adm --config=/etc/origin/master/admin.kubeconfig migrate storage --include=* --confirm
E0315 10:11:30.026186 error:      images/sha256:0270334c4d7adaa8a5dcd592cb219efd13b3c00631184b3a594b329dfd331eec: Image "sha256:0270334c4d7adaa8a5dcd592cb219efd13b3c00631184b3a594b329dfd331eec" is invalid: signatures[0].metadata.annotations: Forbidden: signature annotations cannot be set
E0315 10:11:30.057761 error:      images/sha256:0677366367b1f1a736bdb50b926559c1bdeed02de1bce477f8fe7ed53336a572: Image "sha256:0677366367b1f1a736bdb50b926559c1bdeed02de1bce477f8fe7ed53336a572" is invalid: signatures[0].metadata.annotations: Forbidden: signature annotations cannot be set
E0315 10:11:30.156449 error:      images/sha256:1104dcdacfa9c40222e9256029cafe0b084c8dcc911ab8e816c3f39bd5a4dad1: Image "sha256:1104dcdacfa9c40222e9256029cafe0b084c8dcc911ab8e816c3f39bd5a4dad1" is invalid: signatures[0].metadata.annotations: Forbidden: signature annotations cannot be set
E0315 10:11:30.275157 error:      images/sha256:263c5a1107b6703b3db87f1cb7481a74aa7b7d1138a2da49cb692fa1ec05a42b: Image "sha256:263c5a1107b6703b3db87f1cb7481a74aa7b7d1138a2da49cb692fa1ec05a42b" is invalid: signatures[0].metadata.annotations: Forbidden: signature annotations cannot be set

• The image contains image.openshift.io/managed-signature: "true"