The ability to reserve drives from many DGNS was blocked by the previous
commit modifying the initlabelroutines() (SVN revision 24307).  This commit
adds the following two unit tests:

 Ctape_reserveTest::testCtape_reserveWithCountOf2
 Ctape_reserveTest::testCtape_reserveWith1DgnReservationWithDriveCountOf2

These two tests currently fail (test driven development). The first is a repeat
of trying to reserve drives from more than one DGN, though this time via a
different function Ctape_reservei().  The second and more important test is for
the case of using Ctape_reserve to try and reserve many drives from a single DGN.
In order to pass the unit-tests the Ctape_reserve() function needs to be
modified to return -1 and set serrno to EINVAL if either a DGN or a drive count
is anything other than 1.