Build_oem.sh and build_apt.sh are not returning correct error codes

[tomfukushima]

The scripts have some check_xxx methods that look at the error code returned by the last operation and then return and exit on a failure. However, the exit code that is being returned is always 0 because of some flaw in the logic. That is, the error code needs to be stored in a variable, before it gets cleared by the execution of another statement (in this case, the "if" statement clears it).

Dan Seeman found this error and suggested a fix.

This fix is important for a continuous build system to work; it needs proper exit codes coming back.

[tomfukushima]

r4055