[BUILD] Resolve datarootdir in configure
When using Debian's autoconf 2.61-4 early on in configure the following
definitions occur:

datarootdir='${prefix}/share'
datadir='${datarootdir}'

It seems that unless datarootdir is evaluated, datadir can't be evluated
correctly, though I must confess that I don't really understand why.

I any case, without this patch, I see ${prefix} creeping into
output files, like hbclient.py, but with this patch I see no such problem.

Without this patch I also see the following tell-tale warinings
from configure.

Our Host OS: linux-gnu/i686-pc-linux-gnu
configure: WARNING: datadir directory (${prefix}/share) does not exist!
configure: WARNING: docdir directory (${prefix}/share/doc/heartbeat-2.1.1.1) does not exist!

Signed-off-by: Simon Horman <horms@verge.net.au>

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extra : convert_revision : ee1ab9ae39aa9a7c9b2c1375347adae055596adb