Skip tests known to fail when running under Gentoo sandbox.

--- a/tests/du/long-from-unreadable.sh
+++ b/tests/du/long-from-unreadable.sh
@@ -29,6 +29,9 @@
 # unnecessarily to using FTS_NOCHDIR mode in this corner case.
 
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+# Avoid #413621 until #548250 is resolved
+test -n "$SANDBOX_ACTIVE" && skip_ "Gentoo: Test known bad under sandbox (#413621)"
+
 print_ver_ du
 
 require_perl_
--- a/tests/ls/removed-directory.sh
+++ b/tests/ls/removed-directory.sh
@@ -19,6 +19,9 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+# Avoid #413621 until #548250 is resolved
+test -n "$SANDBOX_ACTIVE" && skip_ "Gentoo: Test known bad under sandbox (#413621)"
+
 print_ver_ ls
 
 case $host_triplet in
--- a/tests/ls/stat-free-symlinks.sh
+++ b/tests/ls/stat-free-symlinks.sh
@@ -17,6 +17,9 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+# Avoid #413621 until #548250 is resolved
+test -n "$SANDBOX_ACTIVE" && skip_ "Gentoo: Test known bad under sandbox (#413621)"
+
 print_ver_ ls
 require_strace_ stat
 
--- a/tests/misc/env-S.pl
+++ b/tests/misc/env-S.pl
@@ -30,6 +30,11 @@ $env = $1;
 # Turn off localization of executable's output.
 @ENV{qw(LANGUAGE LANG LC_ALL)} = ('C') x 3;
 
+# Skip if sandbox is enabled
+if ($ENV{SANDBOX_ACTIVE}) {
+     CuSkip::skip "Gentoo: Test known bad under sandbox (#675802)\n";
+}
+
 my @Tests =
     (
      # Test combination of -S and regular arguments
--- a/tests/rm/deep-2.sh
+++ b/tests/rm/deep-2.sh
@@ -17,6 +17,9 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+# Avoid #413621 until #548250 is resolved
+test -n "$SANDBOX_ACTIVE" && skip_ "Gentoo: Test known bad under sandbox (#413621)"
+
 print_ver_ rm
 require_perl_