Fixes in FVP invocation

[vhscampos]

This patches fixes two bugs:

• Properly propagate FVP's return code to the caller.
• Prepend INST= to the --application argument value. This is required when the application's path contains equal signs (=). This sign is interpreted as a special case inside FVP: its presence in the path leads to ambiguity. One way to work around this is to do the prepend. After that, any = sign that comes up in the path is treated as part of the path.

This is the help message from Corstone's --application:

-a, --application FILE application to load, format: -a [INST=]FILE (use -a INST=FILE for a specific instance, use -a INST*=FILE to match multiple instances using wildcards e.g. for SMP cores)

[dcandler]

The first change is a straightforward fix and looks fine, but I might be missing something for the second: the argument to --application is the path to the image, so why would a path contain an equal sign?

[vhscampos]

There are a few examples under the libcxx tests. For instance, all tests under the directory named
libcxx/test/std/strings/basic.string/string.nonmembers/string_op!=, or libcxx/test/std/iterators/predef.iterators/move.iterators/move.iter.ops/move.iter.op.+=/

[dcandler]

Ah okay, it's coming from libcxx.

From that Corstone help message, the *= operator is intended for matching multiple instances with a wildcard. If we have a specific image that we want to run, should we instead prepend INST=? Including the keyword might also make it easier to understand the context of the argument.

[vhscampos]

Done that. Thanks.