webadmin: Improve attestation status message

This change improves the description of the enum value that indicates
that the data required for attestation of a host hasn't been retrieved
yet.

Change-Id: If444cecc3393a4563b3d6d4a1676dc2db378acf6
Sgined-off-by: Yuko Katabami (方波見裕子) <ykatabam@redhat.com>
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>