gdb/testsuite: avoid stack addresses in test names

When comparing the test results for two different runs of GDB I
noticed a difference in the results for gdb.base/frame-view.exp.

The difference was caused by one of the tests including a stack
address in the test name:

  PASS: gdb.base/frame-view.exp: with_pretty_printer=false: select-frame view 0x7ffff7c5cea8 0x40115b

and

  PASS: gdb.base/frame-view.exp: with_pretty_printer=true: select-frame view 0x7ffff7c5cea8 0x40115b

If for whatever reason the stack address changes between test runs
then it becomes harder to compare results.

Fix this by giving the test a descriptive name that doesn't include a
stack address:

  PASS: gdb.base/frame-view.exp: with_pretty_printer=false: select thread 2 frame from thread 1

and

  PASS: gdb.base/frame-view.exp: with_pretty_printer=true: select thread 2 frame from thread 1

There's no change to what is actually tested after this commit.