use_find_cache: add another pattern

in repo/android/build/core/base_rules.mk
 java_resource_file_groups+= ...
 cd ${TOP_DIR}${LOCAL_PATH}/${dir} && find . -type d -a -name ".svn" -prune \
 -o -type f -a \! -name "*.java" -a \! -name "package.html" -a \! \
 -name "overview.html" -a \! -name ".*.swp" -a \! -name ".DS_Store" \
 -a \! -name "*~" -print )

refactor androidFindCache. add walk method.

% time ./repo/android.sh kati -c > /dev/null
find: `dummy': No such file or directory
find: `dummy': No such file or directory
fatal: Not a git repository: 'packages/apps/Camera2/.git'
./repo/android.sh kati -c > /dev/null  32.38s user 41.67s system 130% cpu 56.897 total
% time ./repo/android.sh kati -c -use_find_cache > /dev/null
fatal: Not a git repository: 'packages/apps/Camera2/.git'
./repo/android.sh kati -c -use_find_cache > /dev/null  33.26s user 18.88s system 153% cpu 33.974 total
2 files changed