test/sanity: No longer return child code

This is so in the event of an error, the suite keeps running.
Makefile: Ignore errors during sanity suite run

run-sanity runs make with -i and -s flags activated, to supprress
output and continue execution in the event of an error. We can
visually see error codes, so there's no need to terminate every
time a unit test fails.
Merge branch 'sanity-test-suite'