Tweak sss-bp-on-user-bp.exp

sss-bp-on-user-bp.c has an assumption that write to integer can be
compiled to a single instruction, which isn't true on some arch, such
as arm.  This test requires setting two breakpoints on two consecutive
instructions, so this patch is to get the address of the next
instruction via disassemble and set the 2nd breakpoint there.  This
approach is portable.

This patch fixes the fails in sss-bp-on-user-bp.exp on arm-none-abi
target.  There is no change in x86 test results.  I also revert the
patch to PR breakpoints/17000, and verified that the patched
sss-bp-on-user-bp.exp still trigger the fail on
x86-with-software-single-step.

gdb/testsuite:

2014-06-04  Yao Qi  <yao@codesourcery.com>

	* gdb.base/sss-bp-on-user-bp.c (main): Remove comments.
	* gdb.base/sss-bp-on-user-bp.exp: Don't set breakpoint on
	"set bar break here".  Get the next instruction address and
	set breakpoint there.  Remove "bar break" from the regexp
	patterns.