btrace, test: fix multi-line btrace tests

btrace, test: fix multi-line btrace tests

For testing multi-line test output, gdb.btrace tests used the following
pattern:

  gdb_test "..." "
  ...\r
  ..."

Change this to:

  gdb_test "..." [join [list \
    "..." \
    "..."] "\r\n"]

Also extract repeated tests into a test function and shorten or remove
test messages.

2014-01-16  Markus Metzger  <markus.t.metzger@intel.com>

testsuite/
	* gdb.btrace/function_call_history.exp: Update
	* gdb.btrace/instruction_history.exp: Update.