sched: fix handling of rt sysctl values
JIRA: https://issues.redhat.com/browse/RHEL-29436
New ltp code tests for various invalid values and edge cases in
a couple of scheduler global tuneables. These patches from v6.6 and v6.7
clean it up.
Tested: Used the ltp test proc_sched_rt01 before and after to confirm.
Signed-off-by: Phil Auld pauld@redhat.com