reflink: fix style problems in existing tests

Fix style problems such as unnecessary use of quotes, add helper
variables to reduce visual clutter, and other minor fixes to make the
first batch of tests more closely resemble the second round tests.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

tests/generic/111

@@ -37,7 +37,7 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
 _cleanup()
 {
     cd /
-    rm -f $tmp.* "$testdir"
+    rm -f $tmp.* $testdir
 }
 
 # get standard environment, filters and checks