Testsuite for libnfs.

To run the tests:
  make VERSION=3 test
or
  make VERSION=4 test
or
  make VERSION=4.2 test

VERSION=4 is NFSv4.0 and VERSION=4.2 is NFSv4.2. The latter needs libnfs
built with NFSv4.2 support, which is the default but can be turned off with
--disable-nfs4-2 or -DENABLE_NFS4_2=OFF.

The tests will ask for your password as it needs sudo access to
run exportfs to create/remove the share we use for testing.
