test/ceph_decoder: add return value check for read_file()

check the return value of read_file function call

Signed-off-by: Xing Lin <xinglin@cs.utah.edu>
test/filestore: add check for return values in StoreTest::SetUp

add return value check for function calls, including mkdir, mkfs and mount

Signed-off-by: Xing Lin <xinglin@cs.utah.edu>