MPI_VERSION check may have false matches

[Jason Sarich]

configure's mpi_version check produces too much output with intel-mpi. The extra grep matches causes a bad Makefile to be written

config/mpi.m4:      MPI_VER=`grep "MPI_VERSION" $mpifile | sed -e "s/#define MPI_VERSION //g" | tr ' ' '\0'`

$ grep "MPI_VERSION" /blues/gpfs/home/software/spack-0.10.1/opt/spack/linux-centos7-x86_64/gcc-7.1.0/intel-mpi-2017.3-ut5hl6baysmb6o26lnds5iimh7dx3djm/compilers_and_libraries_2017.4.196/linux/mpi/intel64/include/mpi.h
#define MPI_VERSION    3
/* I_MPI_VERSION is the version string. I_MPI_NUMVERSION is the
 * I_MPI_VERSION uses the following format:
#define I_MPI_VERSION "2017.0.3"