testcases: ar: Add TST_NEEDS_CMDS on "ar"

In case "ar" binary is not available, the test will fail.
It should return a TCONF as we just do not have the binary.

This commit adds TST_NEEDS_CMDS macro on "ar". Thanks to that,
it will return "TCONF" and not "FAIL" when "ar" is not available.

Signed-off-by: Mylène Josserand <mylene.josserand@bootlin.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
Acked-by: Cyril Hrubis <chrubis@suse.cz>

testcases/commands/ar/ar01

@@ -22,9 +22,12 @@
 #
 # This is a basic ar command test.
 #
+AR="${AR:=ar}"
 TST_CNT=17
 TST_TESTFUNC=test
 TST_NEEDS_TMPDIR=1
+TST_NEEDS_CMDS="$AR"
+
 . tst_test.sh
 
 test1()