fix: logic to compare versions "not installed" with "contain minor"(ex: 20.0.1)

method bulldozer.targets.android.TargetAndroid._install_android_packages()
If build-tools is not installed, then variable "v_build_tools" is string = '0'.
If latest version contains minor version code ~ example 19.0.3 ~, then variable "ver" is list = [19, 0, 3].

In that case, build-tools is not enable to install, because expression([19, 0, 3] > '0') returns False.
Skip invalid name as version in build-tools directory.(ex: .DS_Store)
delete print for debug
Remove duplicated checkbin()
Merge pull request #156 from attakei/patches/resolve_compare_versions

Fixed logic to compare with “non installed” with “minor version upped"
Merge pull request #160 from attakei/master

Remove duplicated checkbin().
allow build folder to be changed