sanity.bbclass: modify check for shell

sanity.bbclass: modify check for shell

Due to the recently implemented update-alternatives for bash binary,
sanity checker may end up with a (false-positive) error such as:

Error, /bin/sh links to /bin/bash.bash, must be dash or bash

This patch modifies the test: presence of "/bash" or "/dash" in shell binary
name results in pass.

[YOCTO#11108]

Signed-off-by: Juro Bystricky <juro.bystricky@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>