qa/rgw: hadoop-s3a uses supported-random-distro$

without this, teuthology-suite tries to schedule against centos8 which
is not supported for squid

Signed-off-by: Casey Bodley <cbodley@redhat.com>

diff --git a/qa/suites/rgw/hadoop-s3a/supported-random-distro$ b/qa/suites/rgw/hadoop-s3a/supported-random-distro$
new file mode 120000 (symlink)
index 0000000..0862b44
--- /dev/null
+++ b/qa/suites/rgw/hadoop-s3a/supported-random-distro$
@@ -0,0 +1 @@
+.qa/distros/supported-random-distro$
\ No newline at end of file