PATCH: make disabling of vfs_snapper consistent with our configure/build system

[Nicolas Pinault]

Hi,

I tried to cross-compile Samba 4.13.0 today.
I got the following error message :
vfs_snapper is enabled but prerequisite dbus-1 package not found. Use 
--with-shared-modules=!vfs_snapper to disable vfs_snapper support.

Using --with-shared-modules=!vfs_snapper I get "bash: !vfs_snapper: 
event not found"
Using --with-shared-modules='!vfs_snapper' has no effect (same error as 
with no option is output).
Using --disable-snapper I get "waf: error: no such option: 
--disable-snapper"

One workaround I found is to remove lines 1945 and 1946 in source3/wscript :
     if host_os.rfind('linux') > -1:
         default_shared_modules.extend(['vfs_snapper'])

Nicolas