Modify gather operation and testdata (#2407)

Modify gather operation and testdata (#2407)

`GeneratedTests.gather_1D_uint8` and `GeneratedTests.gather_2D_uint8` are tests for `gather` operation using quant8 type
However, despite not correctly given test data format, two tests are passed because of weak dataset
And more seriously, `gather` operation do not support quant8 yet
Therefore we should disable the two tests

 - Modify `_uint8` to `_quant8` in test name
 - Modify test data for `GeneratedTests.gather_1D_uint8` and `GeneratedTests.gather_2D_uint8`
 - Disable `GeneratedTests.gather_1D_uint8` and `GeneratedTests.gather_2D_uint8`

Signed-off-by: Seok NamKoong <sk.namkoong@samsung.com>