test: use simple test-config removal in test-common.sh

Piping ls output to egrep in subshell is over the top difficult way to
achieve what can be done with a simple regular expression.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

Closes #138

test/test-common.sh

@@ -22,8 +22,7 @@ import "test-common-selinux.sh"
 import "test-config.$TESTNUM.in"
 cleanup() {
-    rm -f test*.log* anothertest*.log* state test-config. scriptout mail-out compress-args compress-env different*.log*
-    rm -f $(ls | egrep '^test-config.[0-9]+$')
+    rm -f test*.log* anothertest*.log* state test-config. scriptout mail-out compress-args compress-env different*.log* test-config.*[0-9]
     [ -n "$1" ] && echo "Running test $1"
     return 0