Updated the automake min version in autogen.sh to be correct.

The SLURM Makefile.am scripts use pkglibexecdir. One source indicates
that this was not added until automake 1.10.2
(https://github.com/rerun/rerun/issues/167).

So we just made that to be the minimum.
Merge remote-tracking branch 'origin/slurm-2.5'