Disable rsend_020_pos and send-c_volume test cases

The following three test cases occasionally fail the automated
testing.  For the moment disable these test cases until the
underlying issues can be fully investigated and resolved.

rsend_020_pos       - #6086 (32-bit only)
send-c_volume       - #6087 (32-bit only)

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #6086
Issue #6087

tests/zfs-tests/tests/functional/rsend/rsend_019_pos.ksh

@@ -35,6 +35,11 @@
 
 verify_runnable "both"
 
+# See issue: https://github.com/zfsonlinux/zfs/issues/6086
+if is_32bit; then
+	log_unsupported "Test case occasionally fails on 32-bit systems"
+fi
+
 log_assert "Verify resumability of a full and incremental ZFS send/receive " \
     "in the presence of a corrupted stream"
 log_onexit resume_cleanup $sendfs $streamfs

tests/zfs-tests/tests/functional/rsend/send-c_volume.ksh

@@ -35,6 +35,11 @@ function cleanup
 
 verify_runnable "both"
 
+# See issue: https://github.com/zfsonlinux/zfs/issues/6087
+if is_32bit; then
+	log_unsupported "Test case occasionally fails on 32-bit systems"
+fi
+
 log_assert "Verify compressed send works with volumes"
 log_onexit cleanup