Fix check-doxy-blocks.pl to run from root dir
Fix check-doxy-blocks.pl to run from root dir

Modify tests/scripts/check-doxy-blocks.pl to ensure that:
  * It can only be run from the mbed TLS root directory.
  * An error code is returned to the environment when a potential error
    in the source code is found.

ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls