_emergency_shell: Show current working directory correctly in shell.

_emergency_shell: Show current working directory correctly in shell.

When dropped to emergency shell, for example, use rd.break=pre-pivot,
the PS1 won't correctly show current directory we're in:

pre-pivot:/# cd /sysroot/
pre-pivot:/#
(still shows "/")

Let's take a look at PS1 variable:

(I'm adding prefix/suffix 'x' to make it clear):
pre-pivot:/# echo x${PS1}x
xpre-pivot:/# x
(PS1 isn't dynamic)

Regarding the current dracut code, it should be:

pre-pivot:/# cd /sysroot/etc
pre-pivot:/sysroot/etc#

With this patch:

pre-pivot:/# echo x${PS1}x
xpre-pivot:${PWD}# x
(Now PS1 is dynamic, it will show the directory correctly)

I tested for both normal boot and kdump boot.

Signed-off-by: WANG Chao <chaowang@redhat.com>