parser: use private namespace 'graphyy' instead of 'yy'

This can cause linker errors when accessing glusterfs through
libgfapi if the caller also uses a parser with 'yy' prefix.

Change-Id: I6544333c47a1f18193741420717c989e4bdea7b1
BUG: 764890
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5643
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>