Run test build: Rename 'experimental' to 'api_level'

The purpose of the 'experimental' flag is to provide named API level.
Allow the API level to be string or integer instead.

Test: Build artifacts are identical as before.
Change-Id: I15a78979783c1a9237ba9814a48171349e4e5a00
diff --git a/test/807-method-handle-and-mr/build.py b/test/807-method-handle-and-mr/build.py
index d317a1a..027dd53 100644
--- a/test/807-method-handle-and-mr/build.py
+++ b/test/807-method-handle-and-mr/build.py
@@ -15,4 +15,4 @@
 
 
 def build(ctx):
-  ctx.default_build(experimental="method-handles")
+  ctx.default_build(api_level="method-handles")