add --pkg-ccache option

add --pkg-ccache option

1. first build. create _ccache.tar
$ gbs build -A armv7l --ccache

after build is done
_ccache.tar file will be created
BUILD-ROOTS/scratch.armv7l.0/home/abuild/rpmbuild/OTHER/_ccache.tar
backup _ccache.tar file to your storage

2. rebuild with _ccache.tar
$ gbs build -A armv7l --pkg-ccache /path/to/_ccache.tar

test
build chromium-efl
build env: laptop NT371B5M
  - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
  - SAMSUNG MZNLN256 256G SSD

first clean build
gbs build -A armv7l --ccache
build time: 29806s

rebuild
 gbs build -A armv7l --ccache --overwrite --pkg-ccache ~/_ccache.tar
build time: 3294s

rebuild (with qemu-accel (ccache, ninja)
gbs build -A armv7l --ccache --overwrite --pkg-ccache ~/_ccache.tar
build time: 2209s

Change-Id: I5df049e15eaa16a9859c8193a2b922f52406cd44
Signed-off-by: Hyunggi Lee <hyunggi.lee@samsung.com>