Add support in system-test for using user's trust-store

In general, Globus supports two client trust-stores; the system-wide
trust-store (/etc/grid-security/certificates) and a user-specific
trust-store (~/.globus/certificates).  Currently system-test project
copies only the system-wide trust-store.

This can be a problem for people that use the user-specific
trust-store (e.g., they do not have write privileges to the system
trust-store).

This patch adds support for building the test instance's trust-store
by copying certificates from both the system-wide and the user's
trust-store.

Target: trunk
Requires-notes: no
Requires-book: no
Patch: http://rb.dcache.org/r/5707/
Acked-by: Gerd Behrmann