rpm2cpio.sh: make compression tests case-insensitive
In the rpm2cpio.sh script, the output of $COMPRESSION is tested for
certain lowercase strings such as 'xz' in order to determine the
decompression to use. The problem is that the output strings tested
are from the output of 'file', which uses different cases in different
versions e.g. file-5.09 prints:
tmp/sysroots/x86_64-linux/usr/bin$ ./file xxx.tar.xz: XZ compressed data
while file-5.03 prints:
tmp/sysroots/x86_64-linux/usr/bin$ ./file xxx.tar.xz: xz compressed data
In the former, the XZ string causes xz compressed payloads to
incorrectly fall through to the catch-all lzma case.
Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>
