isoimage-isohybrid: don't use TRANSLATED_TARGET_ARCH

isoimage-isohybrid: don't use TRANSLATED_TARGET_ARCH

isoimage-isohybrid plugin fails with this error when
trying to find initrd image:
    initrd = glob.glob('%s/%s*%s.%s' % (initrd_dir, image_name, target_arch, image_type))[0]
    IndexError: list index out of range
as it uses TRANSLATED_TARGET_ARCH value as part of the image.
This approach stopped to work due to changes in oe core code.

initrd file name is made using MACHINE variable. wic can't get value
of this variable as it's not included into bitbake -e output.

Used basename of deploy dir as MACHINE value to fix the breakage.

(From OE-Core rev: cfbb3cc1279ea88ca3e2867f8a409c5120aa1f05)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>