iotests: add hmp helper with logging

iotests: add hmp helper with logging

Minor cleanup for HMP functions; helps with line length and consolidates
HMP helpers through one implementation function.

Although we are adding a universal toggle to turn QMP logging on or off,
many existing callers to hmp functions don't expect that output to be
logged, which causes quite a few changes in the test output.

For now, offer a use_log parameter.

Typing notes:

QMPResponse is just an alias for Dict[str, Any]. It holds no special
meanings and it is not a formal subtype of Dict[str, Any]. It is best
thought of as a lexical synonym.

We may well wish to add stricter subtypes in the future for certain
shapes of data that are not formalized as Python objects, at which point
we can simply retire the alias and allow mypy to more strictly check
usages of the name.

Signed-off-by: John Snow <[email protected]>
Message-Id: <20200331000014[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Reviewed-by: Kevin Wolf <[email protected]>
Signed-off-by: Max Reitz <[email protected]>