PDF Export custom fonts

I had been unable to use a custom font in xhtml2fo.xsl. This seemed similar to XWIKI-2555 but not with the same error message.

In my case on a debian server using tomcat, I was getting:

WARN  o.a.f.a.FOUserAgent            - Font "FreeSerif,normal,400" not found. Substituting with "any,normal,400". 
WARN  o.a.f.a.FOUserAgent            - Font "Times New Roman,normal,400" not found. Substituting with "any,normal,400".

The issue was fixed by manually adding the full path of WEB-INF/fonts directory in the fonts section of fop-config.xml extracted in WEB-INF/classes

     <fonts>
        <!-- Fonts located in WEB-INF/fonts/ are automatically loaded -->
        <directory>/usr/local/tomcat/webapps/xwiki/WEB-INF/fonts</directory>