testsuite, gdb.btrace: make test names unique

gdb/testsuite/ChangeLog:
2020-12-04  Markus Metzger  <markus.t.metzger@intel.com>

	* gdb.btrace/data.exp: Make test names unique.
	* gdb.btrace/delta.exp: Likewise.
	* gdb.btrace/enable.exp: Likewise.
	* gdb.btrace/function_call_history.exp: Likewise.
	* gdb.btrace/nohist.exp: Likewise.
	* gdb.btrace/non-stop.exp: Likewise.
	* gdb.btrace/rn-dl-bind.exp: Likewise.
	* gdb.btrace/step.exp: Likewise.
	* gdb.btrace/stepi.exp: Likewise.
	* gdb.btrace/tailcall.exp: Likewise.