exportfs: getexportent interprets -test-client- as default options

With commit 1374c3861abdc66f3a1410e26cc85f86760b51dd Neil added a
-test-client- export to test the exportability of filesystems when exportfs
is run.  When using the old cache controls (i.e. /proc/fs/nfsd is not
mounted) exportfs will read /proc/fs/nfs/exports to process existing
exports and find these test client entries.  The dash at the beginning of
-test-client- will be cause getexportent to look for default options in the
rest of the string, which test-client- will not match:

exportfs: /proc/fs/nfs/exports:1: unknown keyword "test-client-(rw"

This patch resolves that problem (as Steve suggested) by not processing any
default options if we are reading the list of existing exports from the
kernel.  Default options are converted to individual exports by exportfs so
the kernel won't have any regardless.

Signed-off-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Steve Dickson <steved@redhat.com>