docker: move make check into check_qemu helper

Not all docker images can run the check step. Let's move everything
into a common helper so we don't need to replicate checks in the
future.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

tests/docker/test-debug

@@ -22,5 +22,5 @@ OPTS="--cxx=clang++ --cc=clang --host-cc=clang"
 OPTS="--enable-debug --enable-sanitizers $OPTS"
 
 build_qemu $OPTS
-make $MAKEFLAGS V=1 check
+check_qemu check V=1
 install_qemu