fix bashisms in testsuite/

These places use ${var/search/replace}, $((n++) and
`type -p' constructs which are not-so-standard.
Replace with equivalent constructs.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

testsuite/hostid/hostid-works

@@ -1,8 +1,6 @@
 h=x$(busybox hostid)
 # Is $h a sequence of hex numbers?
-x="${h//[0123456789abcdef]/x}"
-x="${x//xxx/x}"
-x="${x//xxx/x}"
-x="${x//xxx/x}"
-x="${x//xx/x}"
-test x"$x" = x"x"
+case "$h" in
+ x*[!0-9a-f]*) false;;
+ *) true;;
+esac