qa/suites/rados/thrash-old-clients: centos -> ubuntu

We can't upgrade packages from el7 to el8, so do this on ubuntu 18.04.

Signed-off-by: Sage Weil <sage@redhat.com>

diff --git a/qa/suites/rados/thrash-old-clients/distro$/centos_latest.yaml b/qa/suites/rados/thrash-old-clients/distro$/centos_latest.yaml
deleted file mode 120000 (symlink)
index bd9854e..0000000
--- a/qa/suites/rados/thrash-old-clients/distro$/centos_latest.yaml
+++ /dev/null
@@ -1 +0,0 @@
-.qa/distros/supported/centos_latest.yaml
\ No newline at end of file

diff --git a/qa/suites/rados/thrash-old-clients/distro$/ubuntu_latest.yaml b/qa/suites/rados/thrash-old-clients/distro$/ubuntu_latest.yaml
new file mode 120000 (symlink)
index 0000000..3a09f9a
--- /dev/null
+++ b/qa/suites/rados/thrash-old-clients/distro$/ubuntu_latest.yaml
@@ -0,0 +1 @@
+.qa/distros/supported/ubuntu_latest.yaml
\ No newline at end of file