test/encoding/check-generated.sh: run loop in the same shell

test/encoding/check-generated.sh: run loop in the same shell

set parent scope variables in the same shell.

foo | while read ....

in the above statement, `while read ...` is executed in a subshell. so
it cannot change the bash variables in its parent shell.

in this change, the output of `foo` is redirected to the stdin of `while
read` statement. so we can capture the test failures.

before this change, the test always succeed, even if there are failures.

Signed-off-by: Kefu Chai <kchai@redhat.com>