fix to pass run-pass/core-run-destroy.rs on android

[yichoi]

To enable test on android bot #9120

running 4 tests
test test_destroy_once ... task 'test_destroy_once' failed at 'Unhandled condition: io_error: rt::io::IoError{kind: OtherIoError, desc: "no such file or directory", detail: None}', /home/yichoi/rust_latest/src/libstd/condition.rs:131
FAILED
test test_destroy_twice ... task 'test_destroy_twice' failed at 'Unhandled condition: io_error: rt::io::IoError{kind: OtherIoError, desc: "no such file or directory", detail: None}', /home/yichoi/rust_latest/src/libstd/condition.rs:131
FAILED
test test_forced_destroy_actually_kills ... ok
test test_unforced_destroy_actually_kills ... ok

failures:
    test_destroy_once
    test_destroy_twice

test result: FAILED. 2 passed; 2 failed; 0 ignored; 0 measured

task '<main>' failed at 'Some tests failed', /home/yichoi/rust_latest/src/libextra/test.rs:161
task '<unnamed>' failed at 'killed by linked failure', /home/yichoi/rust_latest/src/libstd/rt/kill.rs:639

[alexcrichton]

This is likely because echo isn't actually a program on android.

I think that for almost all of the process tests we should munge the PATH when running on android because this issue seems to come up a lot... That being said, these are just various edge cases, so it may not even need to run on android at all (b/c it's tested elsewhere).