Escaped spaces is supported, so remove the extra filtering of the
isolabel on PPC so that it uses the same form as the other arches.
eg. inst.stage2=hd:LABEL=RHEL-7.7\x20Server.ppc64le for an iso with a
label of 'RHEL-7.7 Server.ppc64le'
Resolves: rhbz#1402328