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.

(From OE-Core rev: fe48e55988a2208bb7a3a2cc2bc641c41dbd1cb0)

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/rpm2cpio.sh

@@ -27,13 +27,13 @@ o=`expr $o + $hdrsize`
 EXTRACTOR="dd if=$pkg ibs=$o skip=1"
 
 COMPRESSION=`($EXTRACTOR |file -) 2>/dev/null`
-if echo $COMPRESSION |grep -q gzip; then
+if echo $COMPRESSION |grep -iq gzip; then
 	DECOMPRESSOR=gunzip
-elif echo $COMPRESSION |grep -q bzip2; then
+elif echo $COMPRESSION |grep -iq bzip2; then
 	DECOMPRESSOR=bunzip2
-elif echo $COMPRESSION |grep -q xz; then
+elif echo $COMPRESSION |grep -iq xz; then
 	DECOMPRESSOR=unxz
-elif echo $COMPRESSION |grep -q cpio; then
+elif echo $COMPRESSION |grep -iq cpio; then
 	DECOMPRESSOR=cat
 else
 	# Most versions of file don't support LZMA, therefore we assume