tests: upgrade: install firefly only on Ubuntu 14.04

The upgrade:hammer-x/f-h-x-offline test installs firefly, but firefly does not
build on CentOS anymore, just Ubuntu 14.04.

References: http://tracker.ceph.com/issues/18089
Signed-off-by: Nathan Cutler <ncutler@suse.com>

diff --git a/qa/suites/upgrade/hammer-x/f-h-x-offline/distros b/qa/suites/upgrade/hammer-x/f-h-x-offline/distros
deleted file mode 120000 (symlink)
index ca99fee..0000000
--- a/qa/suites/upgrade/hammer-x/f-h-x-offline/distros
+++ /dev/null
@@ -1 +0,0 @@
-../../../../distros/supported/
\ No newline at end of file

diff --git a/qa/suites/upgrade/hammer-x/f-h-x-offline/ubuntu_14.04.yaml b/qa/suites/upgrade/hammer-x/f-h-x-offline/ubuntu_14.04.yaml
new file mode 120000 (symlink)
index 0000000..eafeca8
--- /dev/null
+++ b/qa/suites/upgrade/hammer-x/f-h-x-offline/ubuntu_14.04.yaml
@@ -0,0 +1 @@
+../../../../distros/all/ubuntu_14.04.yaml
\ No newline at end of file