Add RHEL7.2 fixes for PR18889 so that we can probe module initializers.

Add RHEL7.2 fixes for PR18889 so that we can probe module initializers.

* runtime/linux/kprobes.c (stapkp_prepare_kprobe): If we have
  kallsyms_on_each_symbol(), just return if we don't have an address.
  (stapkp_prepare_kretprobe): Ditto.
  (stapkp_symbol_callback): New callback function for
  kallsyms_on_each_symbol() to convert symbol_name+offset probes into
  address probes. This works around a kernel bug and should be faster as
  well.
  (stapkp_init): Call kallsyms_on_each_symbol() when needed.
  (stapkp_refresh): Ditto.
* runtime/transport/symbols.c (_stp_module_notifier): Change to the new
  module refresh logic if the kernel version is 3.10 or higher.
* tapsets.cxx (dwarf_derived_probe_group::emit_module_decls): Ditto.
* testsuite/systemtap.base/kmodule.exp: Only run the subtests that load
  the test kernel module after the systemtap module is loaded on systems
  that support module refreshes.