[gbs] Let tizen gbs build use cache properly

[anyj0527]

• Currently only the first arch option use the gbs build cache.
• Remove GBS-ROOT folder when all the tizen gbs build is finished.
• Expecting quite a time boost on gbs build tasks by removing rpm downloading.

Self evaluation:

1. Build test: [ ]Passed [ ]Failed [ ]Skipped
2. Run test: [X]Passed [ ]Failed [ ] Skipped