distro_signatures: add SLES11-SP3

Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
newtests/suse_import_test: add SLES11-SP3 information

Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Merge pull request #411 from nacc/add_sles11sp3_signature

distro_signatures: add SLES11-SP3