REGTEST: adapt some reg tests after renaming.

Some reg tests and their dependencies have been renamed. They may be
referenced by the .vtc files. So, this patch modifies also the references
to these dependencies.
diff --git a/reg-tests/mailers/healthcheckmail.vtc b/reg-tests/mailers/healthcheckmail.vtc
index ed8c2f1..ce3335f 100644
--- a/reg-tests/mailers/healthcheckmail.vtc
+++ b/reg-tests/mailers/healthcheckmail.vtc
@@ -12,7 +12,7 @@
 
 haproxy h1 -conf {
     global
-        lua-load ${testdir}/k_healthcheckmail.lua
+        lua-load ${testdir}/healthcheckmail.lua
 defaults
     frontend femail
         mode tcp