[Android] make_apk.py should not print error messages when search aapt.

On Windows, our code try to find existent executable "aapt" using all possible names, e.g., "aapt.COM", "aapt.exe", and "aapt".
In the search process, we don't need print error message just because a guessed name dosen't exist.

BUG=XWALK-1906
Merge pull request #2070 from iKevinHan/xwalk-1906

[Android] make_apk.py print exception message when search aapt.