qa/suites/rados/perf: pin to 18.04

Caused by a07ca4c5c0f04c43c71231a898c2a89e99a80606

Fixes: https://tracker.ceph.com/issues/49139
Signed-off-by: Neha Ojha <nojha@redhat.com>

diff --git a/qa/suites/rados/perf/ubuntu_18.04.yaml b/qa/suites/rados/perf/ubuntu_18.04.yaml
new file mode 120000 (symlink)
index 0000000..cfb85f1
--- /dev/null
+++ b/qa/suites/rados/perf/ubuntu_18.04.yaml
@@ -0,0 +1 @@
+.qa/distros/all/ubuntu_18.04.yaml
\ No newline at end of file

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