rcutorture/kvm-recheck-*: Improve result directory readability check

The kvm-recheck-(lock|rcu|rcuperf).sh scripts check whether the
user-specified results directory exists.  If not, it prints out error
message that says the specified directory is unreadable.  To make the
message more precise, this commit adds a readability check.

Fixes: 2193e160 ("rcutorture: Abstract kvm-recheck.sh")
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

tools/testing/selftests/rcutorture/bin/kvm-recheck-lock.sh

@@ -23,7 +23,7 @@
 # Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 
 i="$1"
-if test -d $i
+if test -d "$i" -a -r "$i"
 then
 	:
 else

tools/testing/selftests/rcutorture/bin/kvm-recheck-rcu.sh

@@ -23,7 +23,7 @@
 # Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 
 i="$1"
-if test -d $i
+if test -d "$i" -a -r "$i"
 then
 	:
 else

tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuperf.sh

@@ -23,7 +23,7 @@
 # Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 
 i="$1"
-if test -d $i
+if test -d "$i" -a -r "$i"
 then
 	:
 else