genprotimg/check_hostkeydoc: use POSIX compatibility mode

Use the POSIX compatibility mode in a bash shell.

Reviewed-by: Viktor Mihajlovski <mihajlov@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

genprotimg/samples/check_hostkeydoc

@@ -39,6 +39,7 @@ trap cleanup EXIT
 # Enhanced error checking for bash
 if [ -n "${BASH}" ]
 then
+    set -o posix
     set -o pipefail
     set -o nounset
 fi