overlay/017: fix some comments

Align all comments to the term 'constant inode numbers' and
explain why hardlinks are excluded from this test.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

tests/overlay/017

@@ -1,7 +1,7 @@
 #! /bin/bash
 # FSQA Test No. 017
 #
-# Test unstable inode number
+# Test constant inode numbers
 #
 # This simple test demonstrates a known issue with overlayfs:
 # - stat file A shows inode number X
@@ -58,9 +58,8 @@ rm -f $seqres.full
 _scratch_mkfs >>$seqres.full 2>&1
 
 # Create our test files.
-# Not dealing with hardlinks here, because there is more to test
-# then stable inode number.
-# Hardlinks will get a test of their own.
+# Not dealing with hardlinks here, when hardlinks are broken they
+# should not preserve the inode number.
 lowerdir=$OVL_BASE_SCRATCH_MNT/$OVL_LOWER
 mkdir -p $lowerdir
 mkdir $lowerdir/dir