oeqa/runtime/cases/rpm: fix wait_for_no_process_for_user failure case

str.format() doesn't use % notation, update the formatting to work.

assertTrue() is a member of self not a global, and assertTrue(True) will
always pass. Change this to just self.fail() as this is the failure case.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 017f3a0b)
Signed-off-by: Steve Sakoman <steve@sakoman.com>