BL-497 Downloading from BloomLibrary doesn't work

Mono installs mozroots but the certificate library is
initially empty.  This change includes an initial set
of certificates which will make download work.  The
user can run mozroots at any time to update the list.
The mkdir is required because certificate validation
still doesn't work without that directory.  Installation
of mono-devel creates this directory but mono-sil didn't.

Change-Id: I5dc8cfe45a751dbedc5212d5634b68681c896e25