[lldb/Lit] Change the lldbtest format to behave more like shell test.
The current lldbtest format has a number of shortcomings, all related to
how we omit information based on why the test fails. For example, a
successful test would print nothing, even when -a is passed to lit.
It's not up to the test format to decide whether to print something or
not, that's handled by lit itself. For other test results we would
sometimes print stdout & stderr, but not always, such as when a timeout
was reached or we couldn't parse the dotest output.
This patch changes the lldbtest format and makes it behave more like
lit. We now always print the dotest invocation, the exit code, the
output to stdout & stderr. If you're used to dealing with ShTests in
lit, this will feel all very familiar.
Differential revision: https://reviews.llvm.org/D73384