oeqa/runtime/ima.py : fix case issue if IMA disabled
oeqa/runtime/ima.py : fix case issue if IMA disabled

/bin/sh is a symbolic link , so it always get 'Text file busy' no matter
IMA disabled or not.

So this fix uses a binary that really exist to check this.

Signed-off-by: Wu Dawei <b8fdb5b9f0b6b29b63287bce074c688ca08d8ead@intel.com>

01org/meta-intel-iot-security,01org/meta-intel-iot-security,01org/meta-intel-iot-security,01org/meta-intel-iot-security