RFE: Add tests for inheritance across domain-changing exec: siginh, rlimitinh.

[stephensmalley]

Add tests for inheritance across domain-changing exec: siginh, rlimitinh.
There are already basic tests of domain transition (domain_trans), entrypoint, share and ptrace checking across exec (execshare, exectrace), fd inheritance (inherit), and AT_SECURE (atsecure) but no tests for signal inheritance / siginh, or resource limit inheritance.

[stephensmalley]

noatsecure test added by 7e762f0. Still need to add tests for siginh and rlimitinh.