mk: tests.mk simplify the method to clean arm testing directory
etc: modify adb_run_wrapper.sh to avoid 'expr' unrecognization at some android devices
etc: add TEST_EXEC_ENV for run-pass to adb_run_wrapper.sh
test: adjust some test cases for rpass on android
libstd: fix stat struct of android (SEGV error from run-pass/stat.rs on android)
etc: adb_run_wrapper rebased
auto merge of #7128 : yichoi/rust/fix_sometc, r=brson

- Fix stat struct for Android (found by SEGV at run-pass/stat.rs)
- Adjust some test cases to rpass for Android 
- Modify some script to rpass for Android