qa: run e2e test on centos only

this change is a follow up of 02b8b0f49059b58db8b2d16fcc647a17d5ecdf43,
which failed to remove the random facet for distro.

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/qa/suites/rados/dashboard/supported-random-distro$ b/qa/suites/rados/dashboard/supported-random-distro$
deleted file mode 120000 (symlink)
index 7cef21e..0000000
--- a/qa/suites/rados/dashboard/supported-random-distro$
+++ /dev/null
@@ -1 +0,0 @@
-../basic/supported-random-distro$
\ No newline at end of file