Export OS_CACERT after sourcing .stackenv file

This makes sure that it is available to subprocesses like the other
authentication data.

Change-Id: I513b7c2620b171ce20a1ceb5536226f3a69f2b82
Closes-Bug: 1760901

Author: jharbott

openrc

@@ -29,6 +29,7 @@ source $RC_DIR/stackrc
 # Load the last env variables if available
 if [[ -r $RC_DIR/.stackenv ]]; then
     source $RC_DIR/.stackenv
+    export OS_CACERT
 fi
 
 # Get some necessary configuration