arm/lib: Factor out asyncio in FVPRunner

FVPRunner relies heavily on asyncio, despite there being very little
concurrent work happening. Additionally, while the runfvp entry point
starts an asyncio runner, it is not practical to have a single asyncio
runtime during testimage, which is fully synchronous.

Refactor to use subprocess.Popen and related functionality. The process
object has a similar interface to its async equivalent.

Cascade the API changes to runfvp and the test target classes.

Issue-Id: SCM-5314
Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Change-Id: I3e7517e8bcbb3b93c41405d43dbd8bd24a9e7eb8
Signed-off-by: Jon Mason <jon.mason@arm.com>

scripts/runfvp

@@ -1,6 +1,5 @@
 #! /usr/bin/env python3
 
-import asyncio
 import os
 import pathlib
 import signal
@@ -47,11 +46,10 @@ def parse_args(arguments):
     logger.debug(f"FVP arguments: {fvp_args}")
     return args, fvp_args
 
-
-async def start_fvp(args, config, extra_args):
+def start_fvp(args, config, extra_args):
     fvp = runner.FVPRunner(logger)
     try:
-        await fvp.start(config, extra_args, args.terminals)
+        fvp.start(config, extra_args, args.terminals)
 
         if args.console:
             fvp.add_line_callback(lambda line: logger.debug(f"FVP output: {line}"))
@@ -59,15 +57,16 @@ async def start_fvp(args, config, extra_args):
             if not expected_terminal:
                 logger.error("--console used but FVP_CONSOLE not set in machine configuration")
                 return 1
-            telnet = await fvp.create_telnet(expected_terminal)
-            await telnet.wait()
+            telnet = fvp.create_telnet(expected_terminal)
+            telnet.wait()
             logger.debug(f"Telnet quit, cancelling tasks")
         else:
             fvp.add_line_callback(lambda line: print(line))
-            await fvp.run()
+            fvp.run()
 
     finally:
-        await fvp.stop()
+        fvp.stop()
+
 
 def runfvp(cli_args):
     args, extra_args = parse_args(cli_args)
@@ -77,14 +76,8 @@ def runfvp(cli_args):
         config_file = conffile.find(args.config)
     logger.debug(f"Loading {config_file}")
     config = conffile.load(config_file)
+    start_fvp(args, config, extra_args)
 
-    try:
-        # When we can assume Py3.7+, this can simply be asyncio.run()
-        loop = asyncio.get_event_loop()
-        return loop.run_until_complete(start_fvp(args, config, extra_args))
-    except asyncio.CancelledError:
-        # This means telnet exited, which isn't an error
-        return 0
 
 if __name__ == "__main__":
     try: