docker: split configure_qemu from build_qemu

This allows some tests that just want to configure QEMU's source tree
to do so.

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/common.rc

@@ -21,7 +21,7 @@ requires()
     done
 }
 
-build_qemu()
+configure_qemu()
 {
     config_opts="--enable-werror \
                  ${TARGET_LIST:+--target-list=${TARGET_LIST}} \
@@ -32,6 +32,11 @@ build_qemu()
     echo $config_opts
     $QEMU_SRC/configure $config_opts || \
         { cat config.log && test_fail "Failed to run 'configure'"; }
+}
+
+build_qemu()
+{
+    configure_qemu $@
     make $MAKEFLAGS
 }