Upgrade to Surefire 2.18

Notably this addresses SUREFIRE-1028 which prevented running single
test methods.

Changelog:

http://mail-archives.apache.org/mod_mbox/maven-announce/201411.mbox/%3CCAK2FUK2o_9oAUcWkAC=pbA5vejMKW0i0Pn9XBBo9cTg2uRFRYg@mail.gmail.com%3E