Giant-libcephfs_magic_numbers

errata: Last PR pulled in other requests accidently.
Getting rid of the magic numbers that were in the mount function of libcephfs.cc by creating a few defines in the file libcephfs.h and replacing the magic numbers with the new defines. I kept same numbers that were previously used. 

Signed-off-by: BJ A Lougee almightybeeij@gmail.com