PR16716: Fix types in syscall.sched_{getscheduler,setscheduler,rr_get_interval}

PR16716: Fix types in syscall.sched_{getscheduler,setscheduler,rr_get_interval}

* tapset/linux/syscalls2.stp (syscall.sched_getscheduler): Fixed types.
  (syscall.sched_setscheduler): Ditto.
  (syscall.sched_rr_get_interval): Fixed nesting and types. Also change
  'argstr' to just have a pointer to the 'struct timespec' value, since
  that is an output parameter and decoding it on input won't produce
  anything of value.
* tapset/linux/nd_syscalls2.stp: Ditto.
* tapset/linux/aux_syscalls.stp (_sched_policy_str): Updated to handle new
  values, including the new SCHED_RESET_ON_FORK flag.
* testsuite/systemtap.syscall/test.tcl (run_one_test): Since execname()
  only returns the first 15 characters of the test program name, truncate
  it.
* testsuite/systemtap.syscall/sched_getscheduler.c: New testcase
* testsuite/systemtap.syscall/sched_rr_get_interval.c: Ditto.
* testsuite/systemtap.syscall/sched_setscheduler.c: Ditto.