Update aapt check to aapt2

default have been changed, and docs are updated

Test: presubmit
Bug: 314921364
(cherry picked from https://android-review.googlesource.com/q/commit:42a4ec4da99037d34660020015000b784a3cf74f)
Merged-In: Ibf055953b47d646477b62dd7102f9f2d6cc52631
Change-Id: Ibf055953b47d646477b62dd7102f9f2d6cc52631
diff --git a/tools/cts-tradefed/etc/cts-tradefed b/tools/cts-tradefed/etc/cts-tradefed
index 47fcea8..4b477d0 100755
--- a/tools/cts-tradefed/etc/cts-tradefed
+++ b/tools/cts-tradefed/etc/cts-tradefed
@@ -36,7 +36,7 @@
     [[ $1 = /* ]] && echo "$1" || echo "$PWD/${1#./}"
 }
 
-checkPath aapt
+checkPath aapt2
 checkPath adb
 checkPath java