[yocto] xsltproc failing to load docbook.xsl

[colin.helliwell at ln-systems.com]

I'm trying to build a package which uses xsltproc, and it's failing to load
docbook.xsl:

|
/home/colin/100051/fsl-community-bsp/build/tmp/sysroots/x86_64-linux/usr/bin
/xsltproc --output man/nmcli.1 --path man --xinclude --nonet --stringparam
man.output.quietly 1 --stringparam funcsynopsis.style ansi --stringparam
man.th.extra1.suppress 1 --stringparam man.authors.section.enabled 0
--stringparam man.copyright.section.enabled 0
http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl
../NetworkManager-1.6.2/man/nmcli.xml
| I/O error : Attempt to load network entity
http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl
| warning: failed to load external entity
"http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl"
| cannot parse
http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl

I guess I could patch out the '--nonet' for this package, but wondered if
there's a correct way to fix this - a recipe dependency needed and/or
something installed on the host system? 
(I've done a 'sudo apt-get install docbook-xsl docbook-xml'; but can't
figure out where it's expecting the file to be)