qa/distros: make centos_latest 7.3

This will fix smithi runs and break vps runs until we get a 7.3 cloud-init
image ready.

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

diff --git a/qa/distros/supported/centos_latest.yaml b/qa/distros/supported/centos_latest.yaml
index 05e1679b997fa3dc007f8f19aae2c163239fb5af..34d81be44770201dba0eabec8127c5ff18d2b29d 120000 (symlink)
--- a/qa/distros/supported/centos_latest.yaml
+++ b/qa/distros/supported/centos_latest.yaml
@@ -1 +1 @@
-../all/centos_7.2.yaml
\ No newline at end of file
+../all/centos_7.3.yaml
\ No newline at end of file