nfs-utils: reverse order of librpcsecgss and libgssglue checks

The check that validates the version of librpcsecgss also needs to
have libgssglue installed.  Without libgssglue, ./configure complains
that it can't find rpcsecgss, even though it's installed.

It also turns out that the error message generated by pkg-config is
more complete than the one we have in aclocal/rpcsec_vers.m4, so just
let those PKG_CHECK_MODULES m4 macros use the default error message.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>