Don't use the hard-coded name libmpi.so -- instead, use
libmpi.<OPAL_DYN_LIB_SUFFIX>, where OPAL_DYN_LIB_SUFFIX was determined
by configure.

Thanks to Ömer Demirel for reporting the issue.

Refs #3905.
Ouch - remove an extraneous line.

Thanks to Tetsuya Mishima for reporting it

cmr=v1.7.4:reviewer=rhc:subject=Remove extraneous line from OOB