selftests/ftrace: Add check for ping command for trigger tests

All these tests depend on the ping command and will fail if it is not
found. Allow tests to specify dependencies on programs through the
'requires' field. Add dependency on 'ping' for some of the trigger
tests.

Link: https://lore.kernel.org/all/20221017104312.16af5467@gandalf.local.home/
Reported-by: Akanksha J N <akanksha@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>